Interconnecting Propane Bulk Tanks as per NFPA 3

[mahara7a]

Hi guys. I'm currently just involved in propane bulk storage sizing and designing course. Here is a case study where I need to design 3 numbers of propane bulk storage each having a capacity of 4000 gallon and be interconnected. The situation is I need to design storage system without using any vaporizer and just using natural vaporization as the ambient temperature at the hypothetical area is quite high. So my question is, is it possible to interconnect the vapor withdrawal line and still function as intended? Is there any reference that I can refer to size the pipe and design the placement of necessary fittings/ valve for this interconnecting pipe. I've kind of look all over NFPA 58 seems cant find any clarification.

Attached is the basic idea of what I'm trying to achieve.

Thanks.

 

[1503-44]

https://www.regoproducts.com/liquid-propane-gas/field-topics/lp-gas-tank-vapor-manifolds/

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

"still function as intended" - what is the intention?

Size which pipe? the main vapour line? sized for your max flow I would have thought.

It's a very basic sketch so no data, pressure, flows, temperatures, instruments, Relief settings etc so a bit difficult to comment further.

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

 

[mahara7a]

Thanks @1503-44 & @LittleInch for the kind replies. Sorry if my question is a bit unclear.

Let me start over. There are 3 question that is really confusing me.

1) Let say the maximum gas demand is 9 MBtu/hr and there are 3 propane tank be used. Is it correct to assume that each of the tank will be serving 3 Mbtu/hr equally? If that is the case, I believe I can just simply solve the pipe sizing using engineering equation or sizing table.

2) As seen in attached image, for vapor withdrawal line, if there is already an excess flow valve (as required based on the url posted by @1503-44), do we still need to install a check valve? Is it wrong that I have concern vapor from interconnected tank flowing back into another tank if there is no check valve present?

3) As on attached image, I also have a confusion on how to size the refilling pipe (liquid line and vapor equalization). For piping after the tank up to 1st stage regulator I believe it is based on the maximum demand. How about the pipe size for refilling line into the tank? Is it based on the maximum demand as well? Usually I saw that this liquid-IN pipe to be around 2" even though the demand is greater. Sorry for this newbies question.

Thanks

 

[EdStainless]

I don't see how you can assume equal draw from each tank.
Maybe size each for 50% of max flow?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

You appear to be assuming that ambient temp will get you all the heat energy you need?

Can't be bothered to work out what 9MBTu/hr equates to in kg of propane and the amount of heat required per tank, but I suggest you do.

Item 1 - No. There will be differences between each tank - one might get more solar radiation for instance. Also one tank might need to be out for some reason so min 50% and more likely use 60% load coming from one tank.

2 - I assume you mean the blue line? An NRV is aways a good idea to prevent flow back where you weren't expecting it

3- Pie size for filling is based on inflow rate from wherever your propane is coming from. Pipeline? Tanker?
Vapour line is based on return vapour to a road tanker if required or vapour being swept out by the incoming liquid, or just pressurise the tank a bit more.

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

 

[1503-44]

Give them your email to download the compliance kit.

https://www.transtechenergy.com/nfpa-58-compliance-kit

I have some more info that I will attach later.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[1503-44]

attached

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[mahara7a]

Sorry for the late follow up. Thanks littleinch, 1503-44 and edstainless for all the helpful replies. Based on the nfpa kit, i now know that it is possible to interconnect multiple tanks even for vapor withdrawal system and the valve arrangement shall be as per suggested in the NFPA Compliance kit. Realistically, the vaporization are not the same for each tank due to factors such as heat transfer rate and etc. However, as a rule of thumb to grossly estimate the tank sizing without considering any liquid withdrawal then the assumption should be sufficient as in real-practical application, it is rare to see multiple propane bulk tank interconnected and just be withdrawn using only vapor withdrawal for high gas demand system.

Thanks again to all of you for the replies.