Total Dynamic Head Question - Really Simple 2

[chemE72]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1593102457/tips/20200625113428002_rck46c.pdf[/url]

Above I have a photo of a system. Nitrogen header pressure is used to transfer liquid from storage vessel to reactor vessel. The piping system is set up where the header is ran above walkways and brought down to a low point for flow meters, then taken back up to the second floor of a building to the reactor.

To calculate total dynamic head, would the 12 foot dip do anything to elevation difference heads? I am not sure if that dip needs to be accounted for when calculating for vertical lift, or if that will only affect frictional losses. I am assuming that calculations assume only initial and final elevation but I just need confirmation. Basically point 1 would be where at the level of the storage tank, and point 2 would be at the discharge into the reactor.

 

[Latexman]

would the 12 foot dip do anything to elevation difference heads?

No. Just account for the length and fittings for frictional losses.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[bimr]

The dip will not do anything for elevation difference heads.

However, the dip may be problematic as it will trap gas, especially if your operation is not continuous. You will have to make some provision to remove the gas as the velocity head will probably not be sufficient to remove the gas.

 

[Latexman]

bimr is right. It may accumulate gas on the upstream side of the dip (elbow pointing down). A jumper using two tees and not two elbows with a normally closed valve in it may be wise. If it's an existing operation, you should already know this. If it's new, it'd be cheap insurance to install it.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[Compositepro]

If the 12' dip fills with gas, it will add 12' to the head on the pump, or in this case, the nitrogen blanket.

 

[georgeverghese]

On startup, when the transfer line all is filled with gas, the required N2 pressure will have to be 24ft plus line losses. When the transfer line is fully liquid primed, required head will drop to 6ft plus a bit more.

 

[1503-44]

Agree with Comopositepro and georgev... It could form a vapor lock that will need that 12' additional head to clear it.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[chemE72]

That makes sense to me as well. I did not consider the vapor trapped added more head to overcome and this could affect the process. Our current system does not have any way around this and it is a batch process. The dip is for access for operations/maintenance to flow meters and a valve for cleanout and then shoots back up to the header. Thank all you guys for your responses.

 

[Compositepro]

You can install a float operated air vent at the top of the dip.