Fuel tank problem

[mvujica]

Our stand-by generator fuel tanks are four 2000 l plastic tanks in arrangement shown in attachment. Gen-set full load fuel consumption is around 230 l/h but average consumption is around 25-30 l/h so 200 l/h gets returned into tanks. After long power outage of 24h we noticed that tank levels are considerably different and if we didn't refill first tank(first to pump) it would run out fuel and consequently stopped the engine. What could be the problem with this configuration of tanks. Do we have to connect separate tanks by extra piping to avoid problems?

 

[Artisi]

There is no rocket science in a simple diesel engine fuel system or so it seemed up till now - luckily it isn't the fuel system for an intercontinetal missile.

BigInch's second post gave the economical workable solution.

 

[MikeHalloran]

Bottom penetrations of fuel tanks are not legal in all jurisdictions, and may be very difficult to make reliable even if they are legal where the tanks are.



Mike Halloran
Pembroke Pines, FL, USA

 

[nhliew]

Good day,

I suggest to install a float valve at the offtake nozzle to shut when the liquid level falls below a certain point (say, 25% liquid level). When tank D is depleted, the valve shuts and the system draws from tank C at highest flow, and so on. This allows the return line to refill tank D.

mvujica, do you have any overflow/spillage problems? Looking at Tank A, inventory is being drawn at the lowest rate. However, return line is filling it up at steady state. If Qin>Qout, where do all the excess fuel go?

 

[MikeHalloran]

I think I've got a way to do it.
Draw from/ return to just one tank as desired.
Connect the rest with siphons so they'll self- level.

Prime each of the siphons by evacuating it with a pump. It doesn't have to be a big pump, because you don't care how long it takes to fill the siphon. It does have to be graceful about passing liquid.

Instead of trying to switch off the priming pump, e.g. by detecting gas|liquid interfaces, just leave each siphon priming pump running. After it's evacuated the siphon, it will continue to draw fuel. ... so run that flow through a polishing filter and dump it in either/any tank.



Mike Halloran
Pembroke Pines, FL, USA

 

[MJCronin]

mvujica....

OMG...Plastic tanks....plastic pipe & valves.... etc etc !!!

You are asking...no, no begging for a disaster with a diesel fuel system.

ASME B31.1 and NFPA-30 ban use of non-metallic materials in these types of installations.

What has your insurance carrier said about the use of plastic ?

Is this a marine or on-shore installation ?

Where is this located ?

With metal tanks, you are allowed to have nozzles at the bottom of the tanks and comply with all codes and standards.

BIGINCH, All diesel mfrs recommend a fuel system with a return line (there is usually an RO at the end of the line). This configuration has been around forever

Remarks anyone ?

-MJC

 

[mvujica]

Thanks all for great advices, I contacted the manufacturer and the problem is that factory connecting kit for tanks is rated for flow of only 20 l/h, our contractor had installed heating oil tanks and never checked the ratings. Obviously this configuration can not withstand flow of 200 plus l/h that our generator's pump is drawing from tanks. BigInch was right from the beginning that pump is always drawing most of fuel from tank D nearest to the pump.
This configuration is approved for flows less than 20 l/h for heating oil burners but not for gen-set of this size hence my only solution is to replace this system.

 

[Artisi]

"my only solution is to replace this system." what a surprise and about time.