7 replies to this topic

[Ghasem.Bashiri]

Dear all
Assume Some general atmoshperic Tank!

I have an inlet line to this tank. This inlet line can be be connected to the Bottom of the tank.
Also this connection can be connected to the top section.
For top section we may need a dip pipe to the bottom section to aviod electrostatic issue.
Also for bottom connection we need a Check valve to avoid back flow.
Is there any general practice for this issue?
When top or when bottom?
General Case: Atmoshperic Tank, With or without blanketing, hydrocarbon or water
Ghasem Bashiri

[kkala]

To my knowledge concerning refineries, liquid tanks have their nozzles at the low area of their cylindrical surface (close to bottom) according to API 650. And as close to the ground as possible (distance specified by tank wall strength of material), to facilitate emptying. This is assumed to be general practice, including hydrocarbons or water (but blanketing shoule be from a nozzle close to top).

Exceptions to this practice have been seen for specific reasons, such as below.
1. Tank close to sea, danger of fuel into the sea in case of valve leakage.
2. Fuel tank loaded by truck.
3. Rather small tanks feeded directly from production units (phosphoric or sulfuric acid), mainly when roof of tanks do not exceed the piperack level.
4. Tanks fed by gravity flow (not always the case in gravity flow).
5. When tanks are also used for thickenning (e.g. for phosphoric acid thickeners).
Splash filling is not recommended in these "exceptions" (except 5).
Probably the rule can be: think of a low nozzle at first, then see whether there is some reason to change opinion (such as mentioned, or other).

[fallah]

To my knowledge concerning refineries, liquid tanks have their nozzles at the low area of their cylindrical surface (close to bottom) according to API 650. And as close to the ground as possible (distance specified by tank wall strength of material), to facilitate emptying.

Post originator asked for location of inlet nozzle but seems your response not refered to it.

Anyway,IMO emptying would be done by the outlet line through outlet nozzle and usually in the case of the inlet nozzle at near the bottom,a check valve should be installed before inlet connection to avoid emptying by reverse flow through inlet line.

Edited by fallah, 07 September 2010 - 12:56 PM.

[Emetovweke Ochuko]

The Inlet line of the tank can either be connected to the top or to the bottom.

When connecting to the bottom the following should be considered:
1. The position of the inlet line must be higher than the position of the outlet line of the tank as well as the water line if the tank will be used to store crude oil.
2. Check valve in addition to either a ball or a gate valve must be installed on the line to prevent backflow.
3. The inlet nozzle must be at least one pipe side lower than the outlet line.

When connecting to the top the following should be considered:
1. The position of the inlet must be lower than the design liquid level and higher than the position of LSH/LSHH
2. There must be adequate pressure to take it to the top of the tank other wise there will be no flow.
3. The line into the tank should be lowered to the bottom.

I hope this will be of help to you.
Regards
Ochuko.

Edited by Art Montemayor, 08 September 2010 - 10:59 AM.

[kkala]

Post originator asked for location of inlet nozzle but seems your response not referred to it.

All nozzles to transfer liquid (either in or out) are usually located close to bottom. Said "exceptions" refer to liquid inlet nozzles. Let it be an additional clarification to the stand posted by kkala of Sep 7th.

[sheiko]

I have seen feed nozzle to the top and botton in LNG plant. Seems like there is a risk of "roll-over" is you feed a lighter LNG at bottom in a tank filled with a heavier LNG.

[djack77494]

In the case of liquified gases, the inlet line often discharges near the top of the vessel. This is to permit cooling of the vapors which might otherwise get much warmer than the lower liquid filled part of the vessel. Remember that the top is exposed to solar radiation and cannot be assumed to be in vapor-liquid equilibrium.

As a general note, there are often good reasons for deviating from "normal" practices, and the reasons for doing so are not always obvious. My best rule fo thumb to all, coming from someone who is frequently critical of rules of thumb, is to first do no harm. Often that means to not change things (as in from a previous design) if you don't have a good reason for doing so. Especially if the previous design is up and successfully running.

[kkala]

A bit more notes of the subject:
1. A diagram of LNG terminal (ship unloading) indicates all lines feed LNG tanks from their top, using either a splashplate or standpipe pipe inside tanks. LNG out comes also from top, through submergible pumps (acting as booster pumps).
2. On the contrary lines in and out for LPG (and similar liquefied gases) in spheres are connected to the lowest part of them (sometimes on a manhole cover), apparently for convenience (short feed line, easiness to empty).
3. It is not recommended to connect water lines close to bottom of hydrocarbon tanks. Backflow will sometime occur, even if two check valves are placed in series, so water side will get contaminated with oil. That is especially true when water is discharged automatically, so that the isolation valve close to tank remains open .
Above refinery practice is applied even for oily water (they do not want more oily in it) and can be generalized to any liquid not accepting any contamination from the stored one.