21 replies to this topic

[Narnia]

Dear All,

For light diesel oil tanks, is it necessary to have heater within tank to keer temp up ?? kindly suggest

For firing into burner, what type of atomizing media will be used, i think this should be compressed air but dont know why, kindly suggest.can steam will be used

Looking forwrd for propmt reponse

Thanks

[kkala]

No, a heater should not be placed in a diesel tank. Fuel oil or tar have high viscosities, so they are heated to facilitate handling. This is not the case of diesel.
It is noted also that flash point of local diesel is 55 oC, so heating can exceed this temperature, creating risk of fire.
Fon standby boiler burners (the boilers normally burn fuel oil) we use compressed air as atomizing medium. See http://www.cheresour...tomizing-steam/. Steam atomization for diesel is met in refineries, but is not so efficient as compressed air. As Nelson understood to say, gas oils and distillate fuels (except naphtha) are not easily atomized through steam, unless mixed with residual fuels (Petroleum refinery engineering, 4th edition 1958, p. 425, the burning of oil fuels).

[Himanshu Sharma]

I would like to clarify the reason for using MP steam i.e steam at the level of 10~12 Kg/cm2 g in refinery as atomizing media.

Let us begin by the fundamental principle of Fuel oil burning

• The oil must be vaporized, since all combustible matter must be converted to a vapor or gas before combustion can take place. This is usually accomplished by the application of heat.
• The oil vapor must be mixed with air in order to have oxygen present for combustion.
• The temperature of the mixture must be increased above the ignition temperature.
• A continuous supply of air and fuel must be provided for continuous combustion.
• The products of combustion must be removed from the combustion chamber.

Separation of oil into small droplets requires the application of energy. In the case
of nozzles, this energy is supplied in the form of pressure ,having said the same ,MP steam pressure level ensures that fuel oil is properly 'atomized' for combustion,air header pressure is normally lower than MP steam so atomization may not be as good as achieved by MP steam.

Other thing is that oil preheats to a certain extent (closer to ignition temp) while being atomized by MP steam ,this is not possible with air that is usually at ambient conditions.

Steam as an atomizing media also helps down to cut down visible soot or carbon black form the flame.(remember shift reaction !)

I am open to hear the arguments in favor of air as atomizing media, may be i can utilize the wisdom gathered in my next refinery design !

I have seen Diesel tanks with steam coils and i consider them a foolish design practice as pointed out by Mr.Kkala.The only argument operation personnel make out is haziness of diesel while temp drops down too much,water dissolved in diesel separates out and give diesel a hazy appearance.This they deal with a slight heating with steam coil though its a risky operation while flash point is 55to 66 Deg C.

Diesel haziness can be dealt with a properly designed diesel coalescer rather than operating dangerously !

[kkala]

1. Steam seems to be most suitable atomizing medium for fuel oil in the general case. But concerning diesel? Two steam boilers were specified in a local refinery (1999, 2009) burning fuel oil. Start up burners were specified for diesel and air as atomizing medium.
-Referred Nelson relates atomizing to foaming. Fuel oil and steam are mixed up in the burner, resulting foam bursts into a fine mist when coming out of the tip.
Residual fuels have better atomizing or foaming properties. Gas oils or distillate fuels do not atomize easily unless mixed with residual fuels (but naphtha can be burnt satisfactorily through a suitable burner tip) (Nelson, loc cit, post No 2).
2. For the two refineries around Athens, we have not designed diesel oil tanks with heating coil (this was confirmed). No such a case have been heard of (at least by me) concerning diesel tanks in other refineries.

Edited by kkala, 24 January 2012 - 06:47 PM.

[S.AHMAD]

1eater in diesel tank is normally not required except for special c ase where the ambient temperature variation such that the ambient temperature possibly falis below the cloud point of diesel.

[kkala]

I have not thought of heating diesel as a means of dehazing it. It is a possibility, but can have risks, as pointed out in post No 3. In a large diameter tank, accurate control of liquid temperature may not be easy through a heating coil at bottom, so local temperature in excess of flash point (for diesel 55 oC, min) may happen. I have seen this difficulty to obtain uniform temperature distribution in black petroleum products, it is also assumed for diesel to a less extent, but advice from somebody with experience would be welcomed. What instrumentation / measures are needed to heat a diesel tank? Blanketing may be a measure, I wonder whether it is applied. Local diesel tanks do not seem to have provision for it.
As said, diesel tank heating seems not to be locally applied. Specs for diesel, probably related to it, call for:
Automotive diesel : Cold filter plugging point (CFPP) max: -5 oC (winter), +5 oC (summer)
Heating diesel: CFPP max : -5 oC (winter), no requirement (summer)
Pour point, max: -9 oC (winter), 0 oC (summer)

Edited by kkala, 26 January 2012 - 01:13 PM.

[S.AHMAD]

As long as the storage temoerature is kept below the flash point, the risk is nothing more than diesel storage without heating medium in a fixed roof tank. If the temperature is above the flash point, any hydrocarbons should be stored in a floating roof tank to minimize tha risk of fire.

[Narnia]

Thanks for such good informations..

It will ne very helpful if you guide me about what minumum distance to be maintained away from diesel tank so that another equipment to be placed and also to make boundary around LDO tank,what are noraml practice regrding these.Your kind input is required on above.thanks

Looking for prompt response.

[kkala]

Referring to post No 7, storing diesel in floating roof tank must be a specific case. I assume (though not clarified) that diesel tank of post No 1 concerns a cone roof tank. In this case, how can we safely heat the content of the tank below diesel flash point? Heating steam can have a temperature of (say) 200 oC and surface liquid temperature (interface between diesel and air in tank) should be below 55 oC. Risk of fire is assumed to increase when liquid level is low, approaching coils; or when ambient temperature is high, e.g. 30 oC. Any kind of agitation brings more uniform temperature, thus lowers the risk (e.g. jet mixers introducing recirculated liquid to the tank).
Steam feeding valve can be controlled by liquid temperature (but if it fails?). High temperature switch can interupt steam supply when liquid temperature gets close to 55 oC, with high temperature alarm before.
So what are the necessary measures and conditions (such as those supposed above) during diesel oil tank heating, actually applied in practice?
Relative risks are more or less presented above.

Edited by kkala, 27 January 2012 - 11:38 AM.

[kkala]

It will ne very helpful if you guide me about what minumum distance to be maintained away from diesel tank so that another equipment to be placed and also to make boundary around LDO tank,what are noraml practice regrding these.Your kind input is required on above.thanks.

You can look, as an example, into http://www.npchse.ne...PS/C-sf-550.pdf '> http://www.npchse.ne...PS/C-sf-550.pdf , appendix A, Tables A.5 and A.6. General trend for safety distances can be generally (not for a diesel tank) seen at http://www.cheresour...-storage-tank/'> http://www.cheresources.com/invision/topic/13803-propane-storage-tank/. Nevertheless local refineries are not understood to apply safety studies yet for the distances between atmospheric storage tanks.

[Narnia]

Looking for some other informations on safety distances

[Narnia]

I have to calculate the area required in case of spill i.e dyke wall requirement.kindly guide me how to calculate that.

Thanks

[breizh]

Narnia ,
Consider this resource or try to find a copy of NFPA 30

http://www.epa.gov/o...vkinpresent.pdf

Hope this helps

Breizh

[Narnia]

above did'nt reflect my answer, i just want to know what should be the height of dyke wall and what should be volume surrounding by dyke wall in case of spillage.

Thanks

[breizh]

You should read the document carefully ! pages 18,19,20 ....

there is an example

Edited by breizh, 02 February 2012 - 01:47 AM.

[Hyper]

Dear all

what s the diffrence between heavy fuel & light fiuel???

is there any diffrence in thier storage tanks??

BR,

[S.AHMAD]

1. The different between heavy and light F.O is their properties e.g. density, pour point, viscosity, heating value, sulfur, ash e.t.c
2. Storage may or may not be the same. However, light F.O can be stored in heavy F.O tanks but heavy F.O may not be stored in light F.O tanks. It depends on the properties specifically the pour point and viscosity.
3. Any oil having pour point of higher than ambient, must have heating system for ease of pumping. Most heavy F.O tanks is equipped with heating system.

Edited by S.AHMAD, 16 April 2012 - 02:12 AM.

[Hyper]

Many thanks,

could you tell me about thier heating system??
is it a heater inside of tank???

does it need to any special insulation???

[fallah]

could you tell me about thier heating system??
is it a heater inside of tank???

Hyper,

The heating system normally is steam coil.

Fallah

[S.AHMAD]

1. Both internal heating (e.g using steam coils) and external heating could be used. But you need to study the pro and cons of each alternative. That is, each has their own advantages and disadvantages. For example, steam coil is cheaper investment but maintenance will be more difficult for example if coils leak. To repair external exchanger would be easier. Surface area for steam coils is larger as co0mpared to heat exchanger. Therefore, requires cost benefit analysis to determine which alternative is better.
2. As mentioned by Fallah, steam coils has been the popular method but do not restrict your mind, explore alternatives.
3. All piping surface of higher than 60C must be insulated for personnel safety and/or for energy saving. Steam traced is normally provided if pour point is high.

Edited by S.AHMAD, 16 April 2012 - 03:33 AM.

[Hyper]

Dear Fallah & Ahmad

first i should be appriciated for your kind replies.

Mr. Ahmad, please be informed that i want to know about storage tank not pipeline.
for tank insulation(for prevent loss of heat-pour point is high for HF), Which methode is common????

[S.AHMAD]

1. Hot tanks for high pour point products are normally insulated for safety and energy conservation.
2. No specific method for insulation

Edited by S.AHMAD, 16 April 2012 - 09:09 PM.