[b]HOW DO I DESIGN A TANK INLET DIFFUSER[/b] 3

[jcoots]

I've recently been approached about the design of an inlet diffuser for a 230ft dia. tank. I've never delt with this before and immediatly told the person that, but I want to know more. Conceptually I understand what a diffuser is supposed to do. What are the design considerations for such an application? Please enlighten me!

As far as this conversation is concerned, the diffuser is only introducing the product into the tank.

Thanks,

 

[BigInch]

What product?
What inlet velocity?
How high above bottom?


Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[JStephen]

If I remember right, API-650 gives a recommended maximum velocity for fluid going into the tank to prevent static build-up, so that's one consideration.

Another issue is the floating roof, if there is one. Probably work best to talk to whoever designed it for recommendations or requirements.

 

[IFRs]

Basically, you want the exit velocity from the diffuser to be no more than 3 feet per second or 1 meter per second. In the simplest form, you just divide the maximum flow rate by the desired exit velocity to get the required area. Round up. Then provide a pipe extension with holes that add up to the required area. I like to not have holes pointing straight down because they stir up crud from the bottom. I also avoid holes on the top so it does not jet upwards and impinge on the floating roof or broach the liquid surface, creating static charges. Include a generous section of blank pipe first to keep turbulence from the tank shell area. If there will be air or vapor entering the diffuser from pigging, line cleaning etc then the design gets a bit more complicated. A 230 foot tank probably has a significantly large fill rate. Huge fill rates may require special attention to some design and construction details. Like BigInch asked, product, fill rate, line size and pipe elevation are required for a better answer. If you want a design and drawings I could help.

 

[jcoots]

Thanks for the input, YOU'VE REALLY HELPED A LOT!

We are in the estimating stage of this tank. The client said they will be providing specifics such as inlet flow rates and inlet location at a later date. I am assuming it will be provided if we get the job. The only additional information I have is this: Tank Dia. 230', Height 32', Double Deck Floater External, Product is Dripolene/Naptha SG=1.0

 

[IFRs]

You can't possibly do a real estimate without the fill rate. About all you could do is figure a pipe the same diameter of the inlet line extending 1/3 of the way into the tank with a bunch of 2" holes along it's length. Include an end plate and supports. Don't weld the supports to both the tank bottom and the diffuser but do restrain it from lifting off the supports. If vapor or gas can get into the line, double the price. My opinion only - proceed with your best judgement

 

[jcoots]

Thanks again. I'll keep your advice in mind.

 

[jcoots]

Question: At what point or circumstances might I want to have the inlet line branch off into multiple outlets in the tank? The reason I ask is that upon talking with one of my field guys on his experience he has seen an inlet line that once inside the tank it spaned to the middle then came to a Tee where it branched in two directions each about half way to the shell and branched again ultimatly having four outlets for the product located relatively evenly throughout the four quadrants of the tank. What could be the reasoning for this?

 

[IFRs]

Sounds like on of mine! Possibly for mixing, maybe for distributing liquid or gas throughout the tank, maybe because the inlet rate was so high that the length of diffuser pipe exceeded the tank diameter, could also be a crude sparger. I have made them for these reason but not often. Still, each tank situation is different and the lonely few demand special solutions for unusual conditions.

 

[BigInch]

Just might be to get a nice even level lift on the roof.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[sony3005]

are there any institutes in india giving training in design as per api standards

 

[JoeTank]

Codewest (

http://www.codeprep.com)

provides training services in API Standards such as API Standards 653, 650 and 510. They are in Houston, Texas, but provide training to clients worldwide.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com