7 replies to this topic

[wojtar]

I would like to know your opinion about the following problem:

 

Is a basin required for liquefied gas storage or not?

The question is due to a very hot discussion with the future owner of butadiene storage (three spherical tanks). Our national regulations are not clear about that problem. They are regulating strictly liquid petroleum products (basin volume etc.). Regarding liquefied gases there is only statement that the ground under tanks should be hardened - nothing more.

 

So, there is a problem with interpretation of such regulations. Should it be a basin with capacity big enough to contain for example the whole volume of the bigest tank or not.

 

The future owner of the storage sais: the basin is not required (high costs) moreover it creates even mor dangerous situation in case of big butadiene leakage.

 

On the other hand we have seen such butadiene storage having deep basin under tanks.

 

Are there any special regulations regarding liquefied gases storage in other countries/your country?

[kkala]

Greek regulations do not require basin under LPG storage, but "direction" of any liquid spill to safe location, <http://www.cheresour...ed-area-needed/> - post no 5.
Ministerial Decree 34458 in Gov gazette 846/31 Dec 1990 (technical specs for refineries and other petroleum industries) roughly reports following (para 3.2.2).
Conventional basin around pressurized LPG storage is not required. Ground shall be compacted or covered with concrete and have a slope to impede any collection of liquid LPG under the storage, ensuring its free transport far from LPG storage and any other dangerous area. For this purpose separation walls up to 900 mm high are required to direct liquid leakage to proper location. To avoid gas pockets, storage area shall be flat (no pits, open channels, etc) with the exception of mentioned walls.
No LPG storage shall be located in an area or basin with a source of heat (e.g. steam pipes), nor in basins containing storage of other substances. 
Personal notes:
Indeed it is safer to remove liquid LPG spill than collect it below a pressurized storage. But this requires safe location of capacity equal to all non flashed LPG, to cover total vessel rupture.
Basic engineering of two local polypropylene spheres (early 1990) had placed them in a common concrete basin (conventional).
No hint at boutadiene storage in the above Ministerial Decree.
This Decree does not refer to EU legislation in the introduction. Clarification of EU legislation on the subject would be useful.
                    
                    

                    

                            Edited by kkala, Today, 08:42 PM.
                            
                       

[Art Montemayor]

Wojtar:

 

Any engineer, code, local regulation, or an owner that insists on having a “basin” situated below a liquefied gas storage tank is, in my experienced opinion, being ludicrous, ignorant, or totally unsafe about what they are requesting.

 

I don’t know what Polish authorities might think about this application, but any experienced or knowledgeable engineer knows that the storage of liquefied gas is in reality the storage of a pressurized liquid regardless of however slight the pressure inside the storage vessel is.  It is the ignorant layperson who “fears” that the tank might develop a leak and actually spill out a liquid product.  This is never the case if we are talking about storing the known, conventional, liquefied gases found in industry: butadiene, ethane, propane, butane, propylene, butylene, LPG, LNG, Oxygen, Nitrogen, Argon, Hydrogen, Carbon Dioxide, Carbon Monoxide, Ammonia, Nitrous Oxide, refrigerants, etc. etc..  I have stored and processed all of these.

 

Should a leak develop below the liquid level in such a storage tank what will happen is that you will have an adiabatic expansion of the liquid and the result will be a mixture of cold liquid and vapor.  However the resulting mixture won’t just conveniently spill or “drip” from the leak source.  The produced mixture will spray or sprout out due to the driving force inherent to the adiabatic expansion.  Next comes the really dangerous scenario: should you successfully catch and contain the cold liquid product, you will create a pool of hazardous (in the case of butadiene or any hydrocarbon) potential fuel that is being vaporized into a flammable and explosive cloud.  All it needs is a spark since it is surrounded by atmospheric air.  This is exactly what happened at the Amuay Refinery in Venezuela last year, killing over 41 people.

 

When you create a pool of vaporizing liquefied gas out in the atmosphere, you are not containing it.  It continues to vaporize and spreads out in all direction, seeking to mix with atmospheric air and thereby creating an explosive mixture.  I would not recommend this to my worse enemy.  It is entirely foolish, in my opinion, to believe that you could ever control or contain an atmospheric pool of a liquefied gas.  The proven methods to mitigate a potential disaster from liquefied hydrocarbon gas leaks is to isolate the tank in a remote area, supply abundant gas sniffers and detectors, install adequate fire fighting equipment and water sprays as well as sufficient alarms and escape routes.  But the best and foremost important step is to have a proven, conservative, and robust process and mechanical design of the tanks.  If you accomplish this first step, you make a leak an unlikely event.

Check this out with Polish Insurance companies to satisfy your concerns.

 

 

 

[wojtar]

Thank you for your answers. We are considering just small, 15 cm high boundary around the area. Unfortunately we have to convince the Environmental Authority etc. Since the regulations are not precise they would require a basin. As Mr Art Montemayor said: they think that we can control such leakage inside the basin.

[kkala]

A brief search seems to suggest that such basin should not be located below the pressurized storage but at some distance according to API 2510A (edition of 1996 found), probably 100 ft far. In this way chance of flame impinging on the vessel is minimized in case of fire; otherwise you risk vessel explosion, in case that rupture has not completely emptied it. HAZOP and mainly safety study can assess and clarify such matters.

 

Previous posts accept creation of liquified gas pool as possible (*). The question posed is whether design shall try to contain this pool. Is there any alternative measure?  The event seems credible, despite all preventive measures (safe mechanical design, firefighting, distances, etc), which of course should be implemented. Let us see results of mentioned brief search. It is noted that query has asked for (statuary) regulations on liquefied gases storage in various countries.

 

1. Mentioned Greek legislation in post no 2 deals also with low pressure refrigerated LPG storage (LPRS), requiring basin around the tank.  Basin must be able to contain 75% of tank capacity if there is one tank (100% of biggest tank in case of up to 3 LPRSes). This differs to pressurized storage; but indicates containment of liquid LPG spillage, being same in temperature and composition as the pool above.

2. "Process-Safety-Considerations-Design-LPG-Pressure-Storage-Vessels.pdf" (from Web), probably reflecting Saudi Aramco's practice, "Impounding Basin / Diking / Catchment Requirements".
Ground is sloped, leakage is collected in impounding basin at some distance.

3. "Std-118SEP2004.doc" (from Web), Chapter 8.0 "Layout of LPG facilities", 8.1.1 "LPG storage".

Spheres and bullets shall be treated as separate groups; LPG storage vessels shall not be located in same dikes with other stored liquid hydrocarbons.

Spillage collection shallow sump shall be located at a distance where the flames from sump fire will not impinge on the vessel.  This distance shall not be less than the diameter of the nearest vessel or 15 meters, whichever is higher.

4. LP Gas Association's "LPGA CoP 1 Bulk LPG storage at fixed installations, Part 1: Design, installation and operation of vessels located above ground" (Jul 1998), found in HSE (UK) web site, can be useful but is not free. Its relevant recommendation from somebody having access would be welcomed.

5. API 2510A (2nd ed, Dec 1996) referring to pressurized LPG vessels, para 2.4 "Drainage and Spill Containment".

-Objectives are to prevent accumulation of liquid under LPG vessel, provide a location for accumulating liquid to minimize risk (if fire occurs) on critical nearby equipment, confine spillage to smallest practical area to reduce vapor cloud size.
- Reference to API standard 2510 is made, para 3.2-3.5, for spill containment requirements. Even though high-vapor pressure LPG may not form a pool when released, the principles of good drainage should nevertheless be considered.

- Impoundment area (IA) may be either inside or outside of a dike surrounding the vessel storage area.

- Liquid capacity  of IA shall be per API 2510 (para 3.2.3.4 or 3.2.4.3). IA should be located at a distance necessary to minimize chance of flame impinging on a vessel, which requires an engineering analysis. There is little risk for distances of about 100 ft, or more.

-Following para 2.5  "Ignition Source Control": All ignition sources must be recognized, identified and restricted to safe (nonhazardous) areas, or contained safe locations.

 

I think it is worthy to get latest editions of API 2510 and API 2510A. These make the most complete source out of those seen, contain more than what reported here, could contribute to safer design.

 

(*) Suppose ambient temperature=10 oC and stored C4H10 going out through a rather big rupture in liquid and vapor phase. 6.1% of liquid C4H10 will be vaporized and this will also entrain liquid droplets in the created mist. When vessel gets atmospheric pressure, remaining liquid C4H10 (0 oC)  will flow by  gravity. Flashing will not be violent since heat transfer from environment will be rather slow. Not having seen such event, it is supposed to occur so. Behaviour of butadiene is expected similar (similar normal boiling point = -4.4 oC).

Attached Files

•  Process-Safety-Considerations-Design-LPG-Pressure-Storage-Vessels.pdf   487.07KB   137 downloads
•  Std-118SEP2004.doc   229.5KB   85 downloads

Edited by kkala, 15 February 2013 - 11:38 AM.

[wojtar]

Thank you Mr Kostas for your effort. This is really valuable piece of information.

[breizh]

Wojtar ,

Consider this resource for Butadiene: http://www.dow.com/p...diene_guide.pdf

 

Breizh

[Art Montemayor]

Breizh:

 

Once again, you've come through with an excellent and specific information source and material.

Thank you for a great contribution.