Feed to 2 purified water storage tanks.

[dtreacy]

I have an interesting problem with regards feeding 2 purified water storage tanks with one generation system.

I'm trying to design a method of delivering purified water from the product line of an EDI to 2 separate storage tanks and back to an RO Break tank. Each storage tank will have its own separate distribution system.
The constraints on the system are as follows:
1. The tanks and associated distribution loops must remain separate systems to each other with the exception of a common feed loop (EDI to RO Break Tank).
2. During periods of no demand from either tank the system must divert water back to the RO Break tank for re-purification.
3. Where one tank is fed with water and the other is not, the section of pipework in between them cannot become a dead leg.
4. All EDI Product (Purified Water) must be available when demand is present.
5. No back pressure is allowed to the EDI stack.

I would be grateful for any comments, descriptions of current set ups or alternative ideas.

Regards
Daragh

 

[quark]

This can be acheived by a circulation loop and pneumatically/solenoid actuated zero dead leg valves. Install level switches in the tanks. The signal from theses level switches will actuate the valves. When the liquid level in the tanks is high, valve will close off and valve opens up whenever the water level in the tanks go to a preset low limit.

With zero dead leg valves, water will always be in circulation. Check websites of Novaseptic and Saunders for various types of zero dead leg valves.

Regards,


Believe it or not : A cobweb with it's strands a pencil width, can catch hold of a concord. All questions directed to Discovery Channel.

 

[dtreacy]

Only one problem with this, is that all EDI product must be available on demand. ie. When a tank opens all water must be feed the tank, thus draining the recirculation line post feed valve. This is due to the fact that we require all the purified water produced.
Is a bit of a difficult problem.

Can I agrue that the drained section of the loop will be sloped to drain and that it will be adiquately flushed with water at various stages?

 

[MedicineEng]

Dear dtreacy:
Let me see if I understood what is your system:
1.You have 1 production skid and two independent distribution loops let's say loop A and B, is that ok?
2.When one of user point A demands PW, you want to divert all you production skid to Tank A, correct?


Consider this:
1. You will have to have always both PW distribution loop pumps working. You cannot have standstill water in a PW loop, and you should have your pipeline permantelly filled with water;
2.I don't know the quality of your PW, (injectable grade or not). Nevertheless you should consider a UV or an ultra filtration in each distribution loop to avoid contamination of the loop
3.Preferably you should make your loop with slope to the distribution tank; In the section between them you will have to choose which tank you want to be the receiver of that PW.
Now regarding your problem:
I think that you can have two pressure transmitters (one in each loop) connected to a 3-way valve and controlled by your skid's PLC. If one user point opens the valve, there will be a pressure drop in the loop and the pressure transmitter will pass the information to the PLC to control the 3-way valve producing water to the loop where the pressure drop was felt.
The only thing that you have to assure is that you cannot have both loops demanding water at the same time or else your PLC will not know what to do.

Hope that helps

PR

 

[dtreacy]

Not necessarily,

My problem is confined purely to the loop feeding 2 tanks (A & B) with purified water from a single generation skid, the loop starts at the EDI has the 2 tanks as use points and returns to the RO Break Tank (Pre RO Unit). Tank filling will be controlled on tank levels.
Each tank will have its own distribution loop. These loops are independent of each other and the tank feed loop.

The problem is that when tank A requests water I want to divert all water into the tank. This will drain all pipe work post tank A.

It has been suggested that this drained section of the line can be considered a dead leg, especially the section between tank A and tank B.

I require either of the following:

A sound argument that proves the draining of the pipe work is acceptable especially in relation to the pipe section A to B.
Or
A plan with no dead legs.

Any ideas?

Daragh

 

[MedicineEng]

Dtreacy:
Now I understand better your system. The dead leag only happens if you have standstill water in a pipe. As far as I see your system, the only section where you have problems might be between tank A and B, because as I said before, you should have one PW circulation pump in each tank so the water will not stop after tank A or B. What is still not clear to me is "These loops are independent of each other and the tank feed loop". Can you please clarify?
From what I see, with that setup, you only have two options:
1-Have stanstill water in the section between tank A and B;
2-Drain that section.

Both options can be problematic with a picky auditor, but in my point of view and assuming you can stay for long periods of time only working with tank A or B, the one that you can defend better is the one of the draining pipe. It is a "muddy" situation but the only way that you can really defend this is if you have good analitical and microbiological results.

PR

 

[dtreacy]

PauloRibeiro,

The 2 tanks are distribution tanks one tank each tank has its own distribution loop associated pumps and lamps. These loops are outside the scope of the problem.

The issue is how to feed the 2 tanks with purified water from the generation system.
I have called this the “feed loop”. It starts from the EDI unit feeds each purified water tank and returns to the RO Break tank where the water is reprocessed by the RO and EDI.
As for These loops are independent of each other and the tank feed loop". I'm not too sure what I was getting at myself. (Sorry!)

Anyway you are right. The issue arises for the section of pipe between the 2 tanks, when Tank A is being filled.

Solution 1: --- Drain section of pipe:
If the section is drained can it still be considered a dead leg. If this solution was to developed a valve sequence would have to be developed to expel all air in the pipework and adequately flush the pipe section.

Solution 2 --- Allow the section to deadleg.
Not really an option as the pipe section will probably be 6m – 8m and I cannot estimate the time periods that pipe section would deadleg.

Solution 3 ---- Allow a percentage (10%) of water to re-circulate back to the RO Break tank when filling Tank A.
This would maintain the troublesome pipe section in a flooded condition and it would have a continuous flow of water passing through it. However as always the engineering compromise is a 10% loss of feed water when filling Tank A.

I think there is no perfect solution for this.


Regards
Daragh

 

[MedicineEng]

Daragh:
Your option of the recirculation water is in terms of GMP wise the best to defend, but it is inneficient and allowing a 10% loss in a raw material as expensive as PW, I don't know if your boss will enjoy it. Maybe you can convince him of buying another system to have it independent. That also depends which is the "grade" of your water. If it is injectable grade, you will have to go for the 10% loss without any doubt. If it is for solids formulation or API's maybe if you have good analitical results you may go for the draining pipe. It is always a question of money vs. risk.

PR

 

[dtreacy]

Hi PauloRibeiro
The 1st tank will feed USP grade purified water to production and the laboratories.
The 2nd tank feeds a WFI still and 2 PSGs. Since these are purification systems in their own right they do not have to be feed with USP grade water. For this water I can generate my own in-house non-compendial grade specification to suit.

I think I have a good argument but its trying to get people convinced that it is legitimate.

Regards
Daragh

 

[skulpa]

Here is a unique idea that I recently saw employed that might solve your problem...

Since you want to take all the water in the PW loop to whichever tank has the demand (or I suppose both if required), you might make a relatively small, valved, by-pass connection between the PW supply and the PW return. The valve will be controlled such that it opens when there is a demand at either tank. As long as the loop isn't too long, the tanks should represent the "path of least resistance" for flow and water will flow in the reverse direction on the return side through the by-pass valve. Using this "trick", the return line won't go stagnant.

Good Luck,
S.Kulpa

 

[clearh2o]

One more suggestion,
At the entry point to each tank use a "T" with a check valve between the "T" and the tank(1psi spring). On the downstream connection of the "T" place the valve. Control the valve to open to 95% allowing a small flow to go past the "T" and thus provide constant recirculation of all sections of pipe, albeit at a slower flow rate.
Best of luck.
athomas