Why are Day Oil Tanks Used?

Day tanks are used for a variety of reasons.
To provide isolation from a main tank to allow for maintenance etc.
To avoid constant pumping over longer distances which may not be so easy to control/monitor.
To allow a visual check/level/flow monitoring.
Having one main tank and several day tanks can make bulk deliveries/handling easier.

Chemical day tanks are also used where a chemical cannot be conveniently mixed or stored in larger volumes for reasons of degradation/settling/overheating etc.

Del

Those are good engineering reasons. I also understand there are some (perhaps archaic?) regulations about not having more than one day's worth of fuel stored next to a possible ignition source.

Day tank is usually one day's reserve fuel when main tank empties. It usually has all the bells and whistles to let you know of a pending situation. That you have one day to resolve it.

An example that I am well aware of is a drilling rig on remote location. Where fuel may be a day away or more. The fuel being used to run the mud pumps that circulate the drilling fluid that removes cuttings from the hole, turns the drilling string, and allows the rig to pull the drilling string from the hole. The driller has to make the decision when to start pulling the drilling string to keep it from getting stuck.

Would you rather have a day to resolve a pending situation or have the situation right now and have to correct it immediately. That is not covering the cost of letting it get that far.

Wow, All good answers so far! And now for my two cents...

I like Del's answer for several more reasons:

For accounting purposes you would not want to receive into a tank that you are operating from.

If you receive your fuel from a pipeline you cannot test the batch like you would a tank truck or car. If you should get a wet, contaminated or otherwise off-spec batch in a pipeline you would need a way to stay in operation while fixing the problem with the main tank.

Drew

When I was looking after remote power generators we used day tanks for a couple of reasons. You had one for each engine thus ensuring a day's worth of fuel if anything happened to the fuel transfer pump from the main tank. If the active engine would shut down to lack of fuel or other fuel problem e.g water in fuel, plugged fuel filter, fire in one engine; the remote low fuel alarm or power shutdown alarm would be given but the standby engine would be able to start up and continue with it's separate day tank. In other words, the two day tanks provide a redundant fuel supply separate from the main tank.

Hi r-d,

Day tanks are found also in marine applications.Especially in the supply of fuel oil to the main engines or boilers. The principal reason being that fuel drawn directly from the bunkers is frequently contaminated with sea water and other impuriries. This fuel is filtered/centrifuged and pre-heated before being transferred to the day tank. This gives the engine(s) and burner(s) a reliable source to work with.

You might consider this approach of benfit in your installation for slightly different reasons;but as has already been said there is safety and security to the process involved by this supply technique.

If you are using a heavy grade fuel oil>3000 seconds then the day tank and outflow heater incorporating a hot return line forms an ideal way of ensuring that the supply of fuel is always at or near to the optimum working temperature which otherwise can present problems when trying to restart the plant after a period of shutdown.

Good luck,

Massey.