3 replies to this topic

[CRF]

Hi there,

Is there standard sizes of LPG storage spherical tanks?
Essentially, all I need to know is the capacity and its diameter for estimating the storage area size in a industrial plant.

I saw that API STD 2510 is specific for design and construction of LPG installations, but unfortunately I couldn't find a free copy of it available in the internet.

We have to storage about 10213 m3 of LPG. Probably, more than one sphere will be necessary.

The LPG is the condensate stream from a distillation column. The LPG condensate conditions are 13 bar and 50C. For LPG storage, I am assuming there is no need to decrease the temperature, but the spheres will be at higher pressure, so that the LPG will be sub cooled and not saturated in the sphere... is that correct?


Thanks for the attention folks

[fallah]

By a fast looking of API 2510 i didn't see any limitation for spherical tank volume and its diameter as well.

If above mentioned conditions (T,P) provides subcooled LPG,and assuming the tank is full of liquid,you have to maintain that conditions,otherwise by temperature increasing (heat exchange with ambient) or pressure decreasing (due to leakage,even gradually) your system tends to go toward saturation condition.

[Art Montemayor]

CRF:

Lets confront each of your questions/comments:

• No, there is no such thing as a “standard” LPG storage sphere. You can make your required storage sphere of any material, diameter, & configuration that you desire – as long as it meets local engineering codes and laws for pressure vessels. In Brasil, these codes and laws are quite specific and readily available. Pressurized storage spheres are nothing new to Brasil.
• You are not going to find a “free” copy of any API Standard or document on the Internet. These documents are only available through the API and their legal distributors. Any other source is a pirated version and automatically illegal. You certainly are not going to find pirated documents in or through our Forums.
• 10,213 m³ of LPG is a HUGE quantity of LPG storage and will probably call for very large spheres – all of which will have to be locally field-constructged. Sphere fabrication and construction is a specialty and there are not too many engineering firms in the world that are qualified and capable of undertaking such large sphere projectgs.
• While your process LPG condensate conditions are 13 bar and 50 ^oC, I can assure you that those will NOT BE the storage conditions. In Brasil, your ambient storage conditions will be more in the order of 30 to 40 ^oC – depending on what part of Brasil you are talking about. You should cool your process fluid to those ambient conditions prior to storage. Brasil is a very large country. I mention this because I know that if this were a real-life application, an optimization study would have to be done to decide on the storage conditions. You are going to be storing LPG at either ambient, saturated conditions or at refrigerated, supercooled conditions. One or the other. You must first decide what will be your storage design conditions.

Supercooled storage has its advantages and disadvantages. Unless you have strong preferences and engineering reasons for picking supercooled, refrigerated storage, I would recommend that you not do that but rather store at ambient, saturated conditions. The difference, in my opinion, will be a lower pressure for the refrigerated storage – but one that will have very little mechanical integrity and will require reinforcing structural steel. Depending on the diameter of the spheres that you select, the wall thickness is limited to 7 – 8 mm as a practical welding limit. Going to a wall thickness of 13 mm might not mean that much extra cost and it will avoid all the mechanical refrigeration and insulation requirements for supercooled storage – conditions that have no payback when one has to distribute the stored product on a country-wide basis.

Therefore, I recommend you attack your problem by resorting to basics:

• Define your scope of work and stick to it;
• Optimize the size of the storage farm in type, size, and number of storage vessels;
• Design the ultimate size of selected sphere(s).

I hope this experience helps.

[kkala]

Looking at work files, I found some data by chance that may be of interest:
1. Gael D. Ulrich (Chemical Engineering, Process Design and Economics, 2nd ed, PP, 2004) reports a "typical maximum size" of 8000 m3 for spherical vessel (Table 4.27, Criteria and data for Preliminary Design of storage vessels). This seems on the high side to me, but it is probably realizable in USA.
2. A letter of 1990 made a choice between one (diameter=23 m) or two (diameter=19.1 m each) propylene spheres of 16 kgf/cm2 g design pressure. Beveling (forming round) 70-80 mm thick steel plates for the former could be done by quite few companies in Western Europe. However beveling 50-60 mm thick steel plates for the latter could be done by much more companies, being on the high side of normal limits. The semi-qualitative conclusion was that total cost of two spheres was less than this of one (the Project was not realized).
3. So a way would be to search for max plate thickness that can be beveled locally (e.g. in Brazil) and decide sphere diameter (and capacity) according to your findings. If resulting sphere size does not look big enough, search (and relevant budget cost) could be extended over a broader area.
4. In that letter of 1990 semi-refrigerated storage to -5 0C was rejected, as not having a total cost advantage compared to simpler non refrigerated storage. However in about 1995 semi refrigerated storage was selected in a similar case, evidently on the ground that vapor cloud created in loss of containment would be less compared to non refrigerated storage.

Edited by kkala, 01 June 2010 - 03:53 PM.