Fuel tank problem
Fuel tank problem
(OP)
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?





RE: Fuel tank problem
Labeling each tank A to D from left to right,
and assuming you start with equal pressure in each tank,
you will have a large pressure drop in the pipe from tank D into the header, so most flow will come from tank D.
If there were equal flow Q, from each tank, you would have 1Q in the header between A and B, 2Q in the header from B to C, 3Q in the header between C and D and 4Q going to the generator. The pressure drop in AB = H, the pressure drop in BC, with twice the velocity, would have to be close to H^2. It won't try to make H^2 when it can simply pull all it wants from tank D.
I think you need to valve each tank and control the flow from each tank. You could possibly do better by connecting the generator take off to the center of the header, but then you would probably draw most all flow from tanks B&C. You might be able to balance flow from each tank, if you ran an individual pipe from each tank directly to the generator, but I don't think that would be an ideal solution.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
Ted
RE: Fuel tank problem
Having the pipe connected to bottom of each tank will work, and it is best to have valves installed so as to isolate the fuel supply from each tank (if desire to isolate the tanks).
Secondly, the fuel supply connection at each tank bottom should be inserted into tank (i.e. 2-4 inches) to avoid any heavy sediment, debris, or water into fuel system piping.
BigInch - please clarify your posting. I believe you meant to state "D to A from left to right" as the leftmost tank has greatest resistance or longest pipe path (assuming constant pipe diameter).
good luck!
-pmover
RE: Fuel tank problem
Assume all tanks have atmospheric pressure (say 15 psi) on equal fluid levels. There is some pressure, say 8 psi (near tank D) in the beginning of the pipe run to the generator.
Then Tank D has the largest pressure drop (pressure drop for me has psi/ft units), since ft is relatively very very short, (15-8)/(basically just the length from bottom of tank).
The largest pressure drop/unit_length will accelerate more fluid from tank D into the header.
The other tanks have the same net pressure drop from fluid level to the 8 psi point near D, but over a much longer length, hence acceleration of fluid out of those tanks is slower, if there is any at all.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
-pmover
RE: Fuel tank problem
What if you're running in emergency mode and get a new load of fuel and it's contaminated? Now ALL the fuel is contaminated.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Fuel tank problem
My solution is to connect them from above using plastic pipes (without drilling the tanks) and purge air using some other pump eventually creating one large tank.
RE: Fuel tank problem
I'd think the initial flows from D would be around 2 times that of C, which is maybe 4 times that of B... but I'm guessing.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
1. Fit a valve to each of the inlet lines and throttle each valve until the the total head loss of each one is equal, this should result in equal drawndown in each tank.
2. Increase the pipe size on all inlet pipes and the header to the point where the friction loss thru the lines in so low it is inconsequential - as an added improvement, in lieu of end connecting the the supply line to the engine centre connect the supply line.
Option 2 is preferred as it is not subject to flow variations.
RE: Fuel tank problem
RE: Fuel tank problem
Do you have a constant speed fuel pump at the generator?
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
RE: Fuel tank problem
Yes. Connect near the bottoms and feed the main fuel line from a low point in the connection piping. I thought that's what I was talking about in my second post.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
Mike Halloran
Pembroke Pines, FL, USA
RE: Fuel tank problem
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Fuel tank problem
RE: Fuel tank problem
Maybe each tank needs a float valve to close the pickup pipe when the tank level reaches some level near empty so that air cannot be drawn from that 'empty' tank and fuel continues to be drawn from another tank.
Ted
RE: Fuel tank problem
I can't figure out how that German system works.
The tanks would be self- leveling with bottom connections, but it may not be legal to do that, or practical, given the difficulty of connecting to plastic tanks.
Mike Halloran
Pembroke Pines, FL, USA
RE: Fuel tank problem
BigInch's second post gave the economical workable solution.
RE: Fuel tank problem
Mike Halloran
Pembroke Pines, FL, USA
RE: Fuel tank problem
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?
RE: Fuel tank problem
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
RE: Fuel tank problem
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
RE: Fuel tank problem
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.
RE: Fuel tank problem