20 replies to this topic

[Afshin445]

Dear All experts,

I try to design a drain connection for a new 10m (D) x 10m (H) storage tank.The Tank foundation is exist and I want to provide a side drain from the Tank to avoid any foundation modification.In this regard, I have two option:

1- Providing Cone up bottom
2- Providing Cone down bottom

As tank has mixer, as per vendor recomendation for option 1 we need at least 3 m low low liquid level, the result will loosing of 30% of gross voulme, also 10% of volume need to consider for freeboard above overflow nozzle (Tank is open top).That means with this design effective volume should be around 50-55% of total gross tank vloume.
2- For option 2, we need to consider a internal piping for using syphoning effect to drain all of tank inventory to cone lowest point.As this drain line should be free drain without any pump, could you advise me how I can be sure all of tank inventory can be drain with this method? For your infrmation existing foundation height is 600 mm above ground.

Thanks
Afshin

Edited by Afshin, 16 April 2012 - 09:22 AM.

[fallah]

2- For option 2, we need to consider a internal piping for using syphoning effect to drain all of tank inventory to cone lowest point.As this drain line should be free drain without any pump, could you advise me how I can be sure all of tank inventory can be drain with this method? For your infrmation existing foundation height is 600 mm above ground.

Afshin,

Want to use syphon drain? If so:
A sketch of the system shows the levels, especially that of the drain nozzle, could be helpful.

Fallah

Edited by fallah, 17 April 2012 - 01:39 AM.

[breizh]

Afshin,
Don't forget on top what fallah requested to submit info about the fluid !
Breizh

[Dacs]

Ultimately even with a siphon drain, you have to have some allowance from the tank floor to the siphon inlet nozzle and you'll have some (albeit little) inventory left even if you've drained it completely.

I'm just wondering, is it not practical just to erect a small sump on the tank for drainage? I realize you mentioned that you want to avoid working on the foundation, but I feel that to drain the tank completely, this is the most effective solution.

[Afshin445]

 Sketch_Drain.xlsx   14.13KB   171 downloads

Afshin,

Want to use syphon drain? If so:
A sketch of the system shows the levels, especially that of the drain nozzle, could be helpful.

Fallah

Dear Fallah,

Enclosed please find drain system typical skecth.

Afshin

Edited by Afshin, 17 April 2012 - 02:55 AM.

[Afshin445]

Afshin,
Don't forget on top what fallah requested to submit info about the fluid !
Breizh

Breizh,
The fluid content is waste water (same water properties) including max. 10 mg/lit (max.) suspended solid.
Afshin

[breizh]

To avoid pluggage , I will keep a nozzle on the side of the vessel , no piping inside .
You may consider to have two nozzles connected one over the other in case .
What is the point to have cone , just a slope to drain out the liquid .
others may have other ideas .

Breizh

[fallah]

Dear Afshin,

At first, as Dacs mentioned, you cannot drain all inventory from the tank. But generally speaking, as long as elevation of the outlet end of drain pipe is below inlet end (inside the tank), you can sure the tank inventory has been reduced till inlet end level.

Fallah

[Afshin445]

To avoid pluggage , I will keep a nozzle on the side of the vessel , no piping inside .
You may consider to have two nozzles connected one over the other in case .
What is the point to have cone , just a slope to drain out the liquid .
others may have other ideas .

Breizh

Dear Breizh,

Can I have your proposed design in sketch format?

Afshin

Edited by Afshin, 17 April 2012 - 03:33 AM.

[Afshin445]

Dear Afshin,

At first, as Dacs mentioned, you cannot drain all inventory from the tank. But generally speaking, as long as elevation of the outlet end of drain pipe is below inlet end (inside the tank), you can sure the tank inventory has been reduced till inlet end level.

Fallah

Dear Fallah,

What's your idea about my proposed design and also Breizh suggestion.

Afshin

[Dacs]

I would not recommend having a "cone down" sloping because you'll need to have a long spool of pipe to drain out the low point, which is at the middle of the tank.

I think it's better to have a "cone up" floor so that you'll end up having the low point at the edge of the tank, thereby minimizing the spool length.

Check with your company specs, you may also be able to place the drain on the pump suction line, provided you'll place an internal piping, similar to what you've provided, although you'll end up with a higher inventory inside, probably with the vortex breaker and stuff in the inlet piping.

I still would want to hear why you can't provide a sump in the first place. Although personally, I have little motivation to completely drain the tank, since it's just waste water (which I assume does not contain any sour gases).

[fallah]

Dear Fallah,

What's your idea about my proposed design and also Breizh suggestion.

Afshin

Dear Afshin,

Breizh suggestion may lead to plugging of nozzle itself rather than inlet of piping inside, because he may mean the elevation of the nozzle being considered as low as possible close to tank bottom.

About your design, considering cone down sloping has been executed at a glance, it looks like having no problem but needs to be more analyzed and evaluated.

Fallah

Edited by fallah, 17 April 2012 - 04:04 AM.

[breizh]

Afshin

This was my proposal , I understand fallah's comments
Breizh

[Afshin445]

Dacs,

First I need to say tank is open roof and reason of drain should be tank or mixer maintenance or inspection.Also I am agree with you about 5m internal tank piping should be long but I think if outlet drain point will be enough lower than pipe inlet point to overcome the pressure drop in pipe the syphon can work.Also as I mentioned at first post cone top lead us to at least 3 m low low liquid level and can't be acceptable design.In this regards,I didn't understand what's advantage of providing drain nozzle in pump suction rather than separate drain nozzle, for me in both design the drain end point should be lower than pipe inlet point, also in this later case there is possibility of solid accumulation in pump suction, and we need more internal piping so pump nozzle elvation is in higher elevation (at least 500 mm above bottom).
About using sump I don't have any idea because I didn't use this method but I think we need to have good slopping in tank bottom toward to sump.I appriciate if you can provide me a simple sketch.

Fallah,

The only thing I affraiding in cone down design is accumalation of particles in cone lowest point may be lead to pluging the internal pipe, but can we turn on the mixer to suspend the particles before draining, you think is it practical?

Breizh,

Thank you for your sketch.In addition of Fallah comment I want to say may be we need to use two mixer in front of each other and it's not compatible with your design.

Afshin

Edited by Afshin, 17 April 2012 - 03:31 PM.

[fallah]

The only thing I affraiding in cone down design is accumalation of particles in cone lowest point may be lead to pluging the internal pipe, but can we turn on the mixer to suspend the particles before draining, you think is it practical?

Afshin,

IMO, it depends on size of suspended particles. If they are not so large in size to be settled in short time, then you can operate the mixer to suspend the accumulated particles and then after mixer turn-off, start to drain by siphon drain. Simultaneous working of the mixer and siphon drain may affect the drain system performance due to vortex at pipe inlet.

Fallah

Edited by fallah, 18 April 2012 - 02:44 AM.

[Afshin445]

Afshin,

IMO, it depends on size of suspended particles. If they are not so large in size to be settled in short time, then you can operate the mixer to suspend the accumulated particles and then after mixer turn-off, start to drain by siphon drain. Simultaneous working of the mixer and siphon drain may affect the drain system performance due to vortex at pipe inlet.

Fallah

Dear Fallah,

Before we will continue this discussion, can I have your idea about drain system design for another waste water tank in urgent basis, this tank is bigger in size about 15 m (dia.) x 10 m (H) without any mixer. If we expect max. 10 mg/lit suspended solid in tank, what is best drain system design. The only constraint is we want to have side drain so we can provide connection for tank draining to vaccum truck in addition of normal route to open drain system.


Thanks
Afshin

Edited by Afshin, 18 April 2012 - 09:27 AM.

[fallah]

Dear Afshin,

With lack of sufficient information about the bottom sloping, availability of sump(s) at the bottom,..., and considering your constraints (side drain, no mixer available,...) at a glance looks like your proposed facilities would do the job.

Fallah

[Afshin445]

Dear Afshin,

With lack of sufficient information about the bottom sloping, availability of sump(s) at the bottom,..., and considering your constraints (side drain, no mixer available,...) at a glance looks like your proposed facilities would do the job.

Fallah

Dear Fallah,

If I am using side drain with cone down same as before tank, with 10 mg/lit solid concentration I expect around 10 kg solid in tank and all can settle in tank lowest point (cone lowest point), you don't think we it should be risk of internal pipe plugging with that solids, solid particle size can be assumed around mesh 30. Also I think the difference in elevation of drain bottom and pipe inlet should be higher than pressure drop in internal pipe, is any method the minimum drain outlet lowest point?

Thanks
Afshin

Edited by Afshin, 19 April 2012 - 10:23 AM.

[fallah]

Dear Afshin,

With such large diameter tank (15 m) would create great area, 10 kg accumulated solid particles (you didn't mention if the sump is available in the tank bottom or not) spreading on the area (but with most thickness in the center) might not lead to inlet pipe plugging. Nevetheless, peiodic cleaning of the tank bottom is needed to prevent the thickness of bottom sludge to become higher than allowable value.

Fallah

[Afshin445]

Dear Fallah,

You replied to my first question in before post but you didn't say anything about 2nd part of question. How I can find the minimum difference between height of inlet of internal piping and lowest point of drain outlet. Tank foundation height is only 600 mm, you think with 8 m, 4" pipe siphon effect is working?

Afshin

Edited by Art Montemayor, 24 April 2012 - 02:34 PM.

[fallah]

How I can find the minimum difference between height of inlet of internal piping and lowest point of drain outlet. Tank foundation height is only 600 mm, you think with 8 m, 4" pipe siphon effect is working? Afshin

Dear Afshin,

Using Benoulli's Equation between point 1 (water surface inside the tank while draining is in progress) and point 2 (drain outlet) along with some simplified assumptions, below relation is derived:

V=sqrt 2*g*h

V: Outlet velocity
h: Elevation difference between water surface inside the tank and drain outlet

Then, you can simply see that for higher "h" you will have higher velocity and following that higher drain flowrate.

Fallah