17 replies to this topic

[ashrafnew2001]

dear all,

I attend to design a storge tank for HFO with a capacity of 1000 m3, what is the best reference that i can depend on?
and i will be glad if you supply me with any information about the design requirments

[ankur2061]

ashrafnew2001,

Your question is not clear. Are you looking for mechanical design of the tank or are you looking to provide dimensions for the tank?

If you are looking for dimensions then it is a simple case of geometry of a cylinder with the bottom portion being a flat plate meaning that the volume of a cylinder be calculated as:

V = pi*D²*L / 4

where:
V = volume of the cylindrical tank, m3
D = inside dia. of the tank, m
L = length of the tank, m

You need to select a diameter and a length such that the tank capacity is more than 1000 m³ to accomodate for vapor space above the liquid level. Some guidelines could be as follows:

Free-board = 20% which means:
total tank capacity = nominal tank capacity / 0.8
where your nominal capacity is 1000 m³ & total capacity includes the vapor space above the liquid level

L/D (length to diameter ratio) = 0.6 to 0.8

By randomly selecting a tank diameter and performing a few trial-and-error calculations based on the above guidelines for L/D ratio and free-board you will have the dimensions for your 1000 m³ HFO tank.

Hope this is what you are looking for since mechanical design of storage tanks is done by mechanical (static) engineers and not by chemical engineers.

Regards,
Ankur.

Edited by ankur2061, 19 September 2011 - 12:47 PM.

[ashrafnew2001]

thank you very much MR. Ankur for your help you gave me every thing i need in your answer

[fallah]

ashrafnew2001,

One facility may need to be considered in such tanks, especially in cold weather, is submerged steam coil for keeping the fuel oil viscosity in prespecified value.

For mechanical design of mentioned tanks, according to its design pressure, API 650 (atmospheric) or API 620 (low pressure) might be applied.

Fallah

[kkala]

Having read previous useful suggestions, following additional notes can be also useful. See also http://www.cheresour...n-storage-tank/. Tank heat losses to ambient equals heat supply by steam in the steady state (design allows for margins, heat losses to ambient depend much on air velocity, not only on temperature).
1. Heavy fuel oil tanks may need heating of their content to be pumpable. Viscosity limit for centrifugal pumps may reportedly be about 3000 cSt , however maximum viscosity in suction lines can be assumed as more or less 220 cSt for API 650 tanks within dikes. So e.g. No 6 fuel oil (bunkers C) needs heating. http://www.engineeri...ils-d_1143.html.
2. There are cases when fuel oil is only locally heated in tank around suction connection. This will be neglected here. Impression is that this is applicable for tanks of capacity bigger than 1000 m3. Advice welcomed.
3. Consequently tank latera walls should be insulated and fuel oil lines heat traced.
Steam coils are commonly applied for heating, despite the risk of roll over (see below) in case of leakage into the oil. For instance, if coil gets holes, steam will locally condensate into the tank and heat its content. Over here fuel oil daily tanks for boilers (30-40 m3) were externally "heat traced" to avoid this risk (once a ceiling blew up), but this steam pipe "winding" is not practical for 1000 m3 tanks.
At any case steam heated tanks are generally acceptable as standard practice, take care of the measures / precautions adopted for the coil in design and applied in construction (e.g. "generous" corrosion allowance, extent of inspected coil radiographies, robust construction, frequent inspection after start up).
4. Usually two steam coils are installed near tank bottom; one operating, the other standby.
5. Since fuel oil contains a small amount of water, it must not approach water boiling point, which would cause boil over. According to local practice, fuel oil temperature should not be higher than 93 oC. A steam cut off vave should automatically stop steam supply, as soon as fuel oil measured temperature approaches this limit.
5. Representative fuel oil temperature is hard to obtain in a fuel oil tank, even of 1000 m3. Four probes of ~ 1.0 m depth from wall could be located along a tank perimeter, at a height lower than tank low low liquid level (LLLL). Vertical multi-measuring proble (for level indication, etc) can also include temperature indication along tank height. Instrument Dept could help on this matter.
6. If fuel oil needs to be heated above its flash point (or close to it, withing (say) 4 oC) , inert gas blanketing has to be applied.
7. If fuel oil is heated below flash point, no blanketing is necessary. However heating steam temperature had better be below 200 oC, to avoid fuel autoignition in case that liquid level is low enough to emerge heating coils from liquid (http://www.engineeri...ures-d_171.html). If this is not practically possible, intall low level alarm (LLA) and low level cut off (LLLS), to stop steam supply before the coils are emerged.
8. Hope above is useful, comments / additions welcomed. A relevant design practice would give additional information.

Note: Roll over is explained in http://www.igu.org/h...er/add11684.pdf but for LNG tanks. Fuel oil tanks in fire can face roll over due to hydrocarbon stratification, but boiling water (having settled previously) is the main cause.

Edited by kkala, 21 September 2011 - 12:31 PM.

[ashrafnew2001]

thank you all for your answers it been realy usefull to me

[Faustini]

So, if I have a 9.000 m³ tank, the steam coil is still practical? What source of energy would be my best option to use in order to keep the coil heated? What about insulation, is glass wool recommended?

Thank you in advance,

[kkala]

Yes, heating coils can be installed for a fuel oil tank tank of mentioned size or bigger. http://www.cheresour...g-and-handling/ '> http://www.cheresour...g-and-handling/ refers to a heated slop tank of 14000 m3 (operating / spare heating coil at bottom, from specialized supplier); it could be a heavy fuel oil tank instead, same principles (but insulation would cover all tank). See posts of this thread for hints that could be useful.
Since Technological Dept deals with insulation, I do not know what type is suitable, but look at http://guide.rockwoo....aspx?page=2104 '> http://guide.rockwoo....aspx?page=2104 and advice from others is welcomed.

[ankur2061]

Faustini,

Following are the recommendations for insulation of heated tanks as per Mobil Standards

The most common types of hot tank insulation, in order of increasing cost, are as follows:

- Sprayed-on polyurethane, spray coated for weather protection, with a maximum service temperature of about 107°C (225°F). This is not recommended due to maintenance problems.

- Fiberglass blanket or board covered by metal jacketing, with maximum service temperature between 121°C (250°F) and 232°C (450°F), depending on materials and design.

- Mineral wool blanket covered by metal jacketing, with maximum service temperature as high as 538°C (1,000°F).

- Panel systems of polyurethane or isocyanurate foam bonded to metal jacketing with a maximum service temperature of 121°C (250°F), or 232°C (450°F) if faced with fiberglass.

- Calcium silicate or other block insulation covered by metal jacketing may be used. However, these are usually so labor-intensive as to be uneconomical.

Extent and Minimum Thickness

Where insulation is required, 25 mm (1 in) is the minimum thickness for practical installation. For liquid temperatures below approximately 77°C (170°F), insulating the roof of cone roof tanks cannot normally be justified economically. Insulating the roof of a floating roof tank is not usually done because of the difficulty of preventing water ponding and leakage into the insulation.

Hope this helps.

Regards,
Ankur.

[Faustini]

Thank you gentlemen, here is my conclusion:

For our IFS 380 tank (30°C pour point/60°C flash point), We'll use steam coils in order to keep the temperature at 55°C. For insulation, rockwool will be used on shell plates (roof excluded) covered by metal jacketing.

One more question:

Where insulation is required, 25 mm (1 in) is the minimum thickness for practical installation

Are we talking about shell plates?

[ankur2061]

Thank you gentlemen, here is my conclusion:

For our IFS 380 tank (30°C pour point/60°C flash point), We'll use steam coils in order to keep the temperature at 55°C. For insulation, rockwool will be used on shell plates (roof excluded) covered by metal jacketing.

One more question:

Where insulation is required, 25 mm (1 in) is the minimum thickness for practical installation

Are we talking about shell plates?

This not only for shell plates but also for dished ends in case a vessel with dished end needs to be insulated . In fact, some tank and vessel insulation contractors keep a stock of pre-fabricated blankets or boards of various thickness, size (Length x Width) and materials.This saves a lot of time and cost for an insulation contractor when awarded an insulation contract. The minimum thickness generally starts from 1 inch.

Hope this helps.

Regards,
Ankur.

[Faustini]

Wow! This is no good. According to my calculations the entire shell plate would have less than 1inch thickness. Installing an insulation will rise our estimation a lot!

[Faustini]

Thank you gentlemen, here is my conclusion:

For our IFS 380 tank (30°C pour point/60°C flash point), We'll use steam coils in order to keep the temperature at 55°C. For insulation, rockwool will be used on shell plates (roof excluded) covered by metal jacketing.

One more question:

Where insulation is required, 25 mm (1 in) is the minimum thickness for practical installation

Are we talking about shell plates?

This not only for shell plates but also for dished ends in case a vessel with dished end needs to be insulated . In fact, some tank and vessel insulation contractors keep a stock of pre-fabricated blankets or boards of various thickness, size (Length x Width) and materials.This saves a lot of time and cost for an insulation contractor when awarded an insulation contract. The minimum thickness generally starts from 1 inch.

Hope this helps.

Regards,
Ankur.

Dear Mr. Ankur,

I hope you are talking about 1inch of insulation thickness, not 1inch of shell plate thickness.

[Faustini]

Isn't external heating better than internal steam coils?

[kkala]

Yes, external steam coil (sort of heat tracing) would be safer but has been seen only in much smaller fuel oil tanks (post no 5, para 3). See <http://www.cheresour...ing-large-tank/> too.

I assume that mentioned external heating is not feasible for a 9000 m3 tank.

Practical experience from others on alternative (except steam)  heating medium in coils of fuel oil tank would be appreciated.

[Faustini]

Indeed, that's what I was thinking. Thank you, Mr. Kostas. Now I have to convince our president not to use external heating. Tough task.

 

But first, I need to give you some valuable information about the region in which the tanks will be installed. Average temperature is 30°C, the area is located near the equator line, next to amazon rainforest. So, climate is hot and humid 365 days a year. I assume heating the fuel oil to a temperature above pour point will not require so much. Still, our president will ask me: are you sure external heating is not practical?

[kkala]

Internal steam coil has the risk of boil over, yet fuel oil tanks in local refineries seem to apply this method of heating. The daily fuel oil tanks for boilers (30-40 m3) make an exception, since they have applied  external coil around the tank (see post no 5).

Alternative heating medium for heating coils (applied in practice) has been requested in post no 15 (flue gases? hot oil? hot water? electric heating?). In local refineries such a case has not been seen though.

[Faustini]

Maybe I'm being a little bit utopic, but: How about solar energy? I'm pretty sure our yard is big enough to fit as many panels we need.