5 replies to this topic

[ELEMAN]

Hello everybody:

I am interested in obtain some knowledge regarding with the phenomenon that occurs when heating heavy fuel oil in an above ground storage tank.

I know that when the fuel is resting in the tank (no flow in and no flow out) the Stokes´s law works very well. But, in order to accelerate the process of settling of solid particles, when some heat is applied to the fuel, an effect (movement) of the fuel in the tank breaks up the rest, maybe hindering the process of settling.

My question: It is needed or not to heat the fuel oil in order to get a better sedimentation? If the answer is yes, does exist a limit of temperature to be reached? How harmful is to heat the fuel for the settling process?

I would like to read documents or find out a web site to look for information. Obviously, any comments on this subject will be highly appreciated.

[Alawi]

Hi,

What do you mean when saying "how harmful is heating to the fuel oil"? The max temperature usually reached in a fuel oil storage tank does not exceed 90 C, to prevent any possibility of sudden water expansion in the tank.

Kind regards

[ELEMAN]

Hi Alawi:

My question in fact was: "how harmful is to heat the fuel oil for the settling process?

My question is regarding with the process of sedimentation, because if the liquid is heated up, a circulation of fuel inside the tank is induced so, solid particles and water are in movement, and the precipitation is disrupted.

Another way to ask the same question: Is it needed or not to heat the fuel inside the tank in order to get some precipitation of solids particles and water? Is it okay to leave the fuel at ambient temperature for the same purpose? (in the location of these fuel tanks, the ambient temperature is around 35º C and 40º C all the year).

Thanks.

[dinesh]

hii,

i got your question,
generaly it is better to provide heat in the tank by means of providing the heating coil in the tank to enhance the settling of the Heavy solid particles by means of reducing its viscocity.
But the temp of the coil is depend upon the flash pioint of the liquid that is being stored in the tank.
anather way to answer you that u can leave the Heavy Fuel Oil in the tank for a year as it is,
but for unloading purpose u must have to provide heat in the tank.

Thanks,
Dinesh

[Adriaan]

Wouldn't the heating of the oil cause separation between different components of the oil?

I ask because we have had problems with that, heavier fractions lower down that - after a tank wasn't used for some time - caused problems in our process. I'd imagine that YOU could have some problem when (partially) unloading a tank for the same reason?

[JMW]

In discussing Heavy fuel oil handling in storage I have been advised (my comments are for consideration, and based in indirect experience) that the Major oil companies tend to use tank mixers to maintain the fuels homogeneous (and preserve their quality as per the certificates).
Heavy fuel oils are mostly blended fuels and, with the introduction of MARPOL, marine fuels are increasingly blended with higher density cutter stocks.
Over time the fuels will not only stratify but they will also settle out. There may be added problems if the fuel components are not compatible and since, for marine fuels at least, most blends are of imported fuels stocks from different sources the problem is a common one. However, some blends are produced as the fuel is supplied so the problems may not be apparent unless, as is recommended, the fuels are tested for computability. In any event, over time, the fuels will tend to separate (not just Heavy fuel oil).
In terminals and fuel storage depots it is not always the case that there are tank mixers and not only do the fuels stratify the also do separate. Also, because there is a tendency to add new batches of fuel to tanks containing a residual amount of previous batches, if the older fuels are lighter, they tend to become trapped in storage for longer enhancing the potential that separation will occur.
When separation does occur, the lighter components rise to the top and remain and the heavier components fall to the bottom.
This means that fuel quality, as taken from storage, can be very suspect. One operator told me he had taken top, middle and bottom samples from his 380cst fuel storage and found the viscosity varied from around 150cst to 415cst.
Of course, sludge will collect in the bottom anyway.
How often is it cleared out?
I would guess that the bulk of Heavy Fuel oils are turned over fairly rapidly but where it is a stand by fuel or a start up fuel, it may stand for longer periods and I would suspect that fuel handling procedures would necessarily have to allow for this.
Incidentally, heating the fuel reduces the viscosity and the lower the viscosity, the less the residence time for solids and air bubbles in the fuel so I would suggest that moderate heating will enhance the settling process without generating sufficient circulation to impede it.