Preventing or Minimizing Foam Formation

Hmmm.

Clearly, whatever minimises gas entrainment would be a good thing for this process, and further experimentation would pay dividends. Also, many years ago, a foam problem was minimised by spraying on an additive. If the product will stand it and its surface is accessible, a mixture of n-butanol and n-octanol applied intermittently with a garden hand-sprayer was quite good at getting rid of surface foaming. Without knowing what the product in these particular tanks it is diffcult to make a specific recommendation and the toxicity data in respect of these materials would need to be assessed before commencing treatment. There is flammability to consider in respect of these materials also.

It seems tank 2 and 3 will be a good alternative - however if your are pumping at high flowrates and head, the 3rd design might cause erosion of the tank wall.

One thing to consider will be the piping prior the tank and pump. Is there some way that air is introduced into the system? Leaks at the inlet side? Is the head from the pump inlet to source high?

I work for Chemicalcontrols.co.uk we produce dosing systems (not chemicals) but have done several applications where the customer was dosing relatively small volumes of anti-foaming agent in applications like vegetable washing.

So there are obviously chemicals for this specific purpose.

I'm thinking along the lines of Solrac; is the foaming due to a chemical or thermal reaction or is it due to aeration? If it is aeration, then it would be caused by the method and rate of delivery to the tank.

A weir valve arrangement in the tank might help the liquid settle and give specific areas from which the foam could be controlled.

Okay, a little more information is called for.

I don't want to specifically mention what the liquid is, except that it naturally generates carbon dioxide as a by-product. The suggestion to use anti-foaming agents (my suggestion) was vehemently opposed (by everyone, I might add. Stopped me from suggesting anything further in that meeting). So anti-foaming agents are out.

So far the solution offered was to drop the temperature (keep the CO₂ in solution). The R&D people are still considering that but I was thinking that if a simple piping change could solve or minimize it, then we won't have to change the temperature or maybe just change it by a little bit.

I don't know the velocity of the liquid but I've watched it as it enters the tank and it's not very vigorous. One tank has the inlet pipe pointing into the tank wall but it still foams a lot. The end of the pipe is at the middle of the tank, however, instead of at the bottom. I don't know if moving it to the bottom will help.

Solrac is right. Reducing the Reynolds number is key. You have to drop it by any means, e.g. a value of 1800 is for sure too large. E.g. water from a 1" pipe at 3 ft/sec has already Re ~2500. And, of course, the delivery pipe-head should be always immersed (else the liquid will accelerate in free fall).

You can fit a flat delivery head with a narrow slit, such that (h x b) = pi/4 x d^2, i.e. the slit area is equal to your delivery pipe (it minimizes the turbulence). If d = 10 x (2h) than Re(slit) = 0.1 x Re(pipe).

There is another "catch" with keeping the area constant: any acceleration of the fluid drops the pressure locally, which encourages the bubble formation (cavitation-like). Following the same line of thought, you may increase the pressure both in the tank and the in the supply system (which you may inspect for sharp elbows or sudden section changes, T-offs without proper reduction, etc.)

It would be interesting to know what type of pump is used. A centrifugal pump would cause more cavitation than say a piston type, screw or mono pump, discharging into bottom of tank is a good idea, however if possible discharge into tank from base with a long horizontal run before entering tank.

You mean like this?

More like this. The horizontal infeed section is longer.

You should have used the nerve pinch at that meeting...

hmmmm... this sounds like a carbonated beverage..... in that case anti-foaming chemicals may be undesireable.

I remember being taught to pour beer down the side of the glass to prevent foaming, would that be a clue?

Another thought/theory: foaming in carbonted beverages (when you shake the container) is caused by the CO2 in the liquid trying to rise, and along with the C02, some liquid is pulled up for the ride, thus the foam. So in the case of one pipe, if the flow of the fluid in the pipe is turbulent, then the CO2 will naturaly try to separate. Maybe if you prevent the flow in the pipe from being turbulent, this can be avoid. My fluid mechanics is a bit rusty, but if I remember correctly, a lower flowrate can make the fluid approach laminar flow. To lower the flowrate in one pipe, use more pipes,(like branching them out) to distribute the flowrate to each pipe (Instead of one big pipe giving out 10 gpm, have 10 pipes give out 1 gpm each). Of course by adding elbows and other fittings, this will tend to increase the turbulence, but with some careful considerations in terms of the pipe diameter and design, I think you can get the Reynolds number to decrease once the fluid is at the end of the pipes.

Just thinking out loud here.... maybe someone more qualified can verify the thoughts.

Solrac wrote: I remember being taught to pour beer down the side of the glass to prevent foaming, would that be a clue?"

REPLY That was my first thought! I would definitely suggest proceeding to the nearest pub where you can do an intensive study of the bar maids pouring drafts into pitchers and study their technique for defoaming the contents. some kind of objective and comparative study is called for. Suggest you replicate the tank arrangement at the tap and document the foam creation or lack therof.

Take copious notes. reread after sobering up and then edit for clarity before submitting to the boss. < grin >

Cheers

Now that's R&D! I assume the associated research costs (beer, nuts and tips) can be charged to the company :-)

Uhm, you mean like tip the glass a little and pour down the side of the glass?

For some reason I don't think the big bosses would like to see our tanks canted over like a beer mug .

It is iinteresting problem. I would suggest following;-

1) Definitely pipe diverted to wall at the bottom. I would say there should be some space left out for release of entrapped gases. Some baffle wall to separate air entrapped liquid so that air goes out. ( Some one suggetsed as to beer is dropped in gas).

2) Low rpm pumps would be better tonreduce foam. Rciprocating would be better compared to centrifugal.

3) NaOCl can be added to reduce foam but depends on what is the liquid.

4) separate de-foamers are in market which subside the foaming effect.

5) Design in such a way that some free legth is avaialble at top so that there is no spill over.

6) Reduce the pressure of liquid and it should hit wall and entrapped air to let go- That is in brief guide to design.

Hi !

The best way is to use defoamers. There are food grade defosmers also available. I know of one company by the name Bussetti & Co GmbH which is in Austria who manufacture all dorts of defoamers. Please check their site for more technical details.

Regards,

Jayant

I know that secrecy is a real pain in times like these but I can't say what we're producing. There's nothing illegal or top secret about it but I do have to be careful about what I divulge. Actually, you may be using our product right now as you're reading this.

Anti-foaming or defoaming agents, food grade or not, is out. We have to be careful about what we put into our product. If it goes into the product, we have to declare it on the label and to the government agencies in charge of such things. Plus the fact that we have to stop normal production to perform tests on the product with anti-foaming agents mixed in.

Indeed, inlet tubes below the surface. Also, I remember the old idea of tapping the can of a carbonated beverage with the fingernails before opening. I can say from experience than I recall never having a foam-out from any can I used this procedure on. I must say I never was brave to really test the idea by shaking the can first! But some got some pretty rough treatment before hand.

So, may some source of vibration at just the right frequency coax the diffusion of gasses back into the liquid?

I'm not aware of that technique. However, that only supposedly works for liquids that are in the can already. We're putting the liquid into the can, not out of it.

Still, that was an interesting tidbit. I might try that sometime.

Totally agree with you on tapping the can! In fact, most of my friends thought this was a weird mannerism of mine prior opening cans (specially from vendo machines). Until I explained and demonstrated to them.... maybe we can start a can tapping cult :-)

Trying to come up with a theory about it though - when you tap the can, you force the CO2 up to the surface faster, and since the can is still sealed while you do this, the volume on top of the liquid is pressurized, preventing most of the liquid which would normally attach itself to the CO2 bubble from foaming. Then, when you open it, since most of the CO2 is already on top of the liquid as CO2 gas, it's just the CO2 which escapes.

Vulcan- This type of foaming problem is prevalent in the Oil & Gas Industry in Transfer operations. I have been out of the industry now for a while but do remember that there were several nozzle and baffle designs out there that minimized or eliminated the problem. You may want to snoop across industry lines.

What about accepting the head as inevitable and just making sure it is all routed out of one opening (notch) near the top of the tank. You may need to make a light weight (removable, for cleaning) cover to force the lighter foam out the side into the foam holding tank (where it can be treated if necessary without contaminating the product)

More information necessary!

We have nine tanks in all. I think the foam holding tank might be bigger than all the other tanks put together .

Also remember that the foam is just product that has a bubble of air (or CO₂) in it. If we can collapse the bubble or prevent it from forming instead of letting it just flow out onto the floor, we prevent losses. Plus the fact that foam on the floor needs to be washed away and diverted to the waste water system for treatment.

Our WWTP is working overtime just to treat this thing. If we prevent the foam from coming out, we reduce our cleaning water use, reduce our treatment costs, and eliminate loss of perfectly good product.

I have seen this work. ...... Divert a portion of the inlet flow through a spray head (like a shower head) direct it on the surface of the tank you are filling. The spray will tend to break up the foam. You will have to experiment a bit with the coarsness of the spray.

Admittedly my initial comment about place to do R&D was slightly flippant, but the idea was serious. I used to work for a company whose owner had invented a drink dispenser nozzle that did remove the foaming effect. So while you cannot tilt the large tanks, the position and placemnt of the nozzle could prove to be a significant factor. Presumably most carbonated liquids will exhibit similar behaviour when dispensed into a large container. If you dig deeper you may in fact find some obscure R&D paper published a long time ago. In Canada and GB the subject has received serious consideration. Witness my former bosses product development. We manufactured an electronic system for order capture in restaurants and the drink dispenser was remotely triggered from the order input ccomputer

Way ahead of its time - unfortunately

Hmm, interesting. I'll note that down. They may want to try it. Thanks.

O.K., I will throw this out there. what reaction will we get if the the tank is a vacuum?

Yes, we do have suction lines (we call them de-gassing lines) for all the tanks. Presumably, the vacuum will cause the bubbles to burst as they form. Also, any CO2 in solution will come out as bubbles but the vacuum should cause them to collapse immediately.

I'll have to get back to you on that. I don't know if the tanks are actually in partial vacuum or not.

http://www.google.com/search?hl=en&q=silicone+%2Bantifoam&btnG=Google+Search

The foam appears when turbulence is present, to avoid foam formation you can try to achieve laminar flow or pseudo laminar, to achieve thisyou have to take down the Reynolds number, your initial apreciation is correct and it helps to reduce the turbulence, if at this submerged pipe you can add to the interior a series of seperations creating a bunch of pipes inside the main pipe it will take down the Reynolds number and will help you achieve pseudo laminar flow (it can be in the last part of the inlet pipe).

Other solution colud be make holes a long the inlet pipe something similar to a flaute, it will be easy and cheaper but the results won´t be as good either.

Perhaps you can pour the liquid down the side of the glass, or at least get the same effect. Attach a circular pipe to the inside upper end of the tank. Drill several holes in it along its circumference, angle these holes so that the liquid squirts onto the side of the tank, you would want a fairly slow flow rate. Allow the liquid to flow down the sides of the tank. This would reduce turbulance and reduce foam formation.

ddm

The foam persists when the surface tension, partial pressure of the fluid and viscosity minimize breakage. In very dry air water based bubbles thin and break.

Silicone anti foams introduce film defects into the bubbles and they pop.

paints will not tolerate silicone antifoams as they interfere with film formation.

Often foam control consists of not makiing it in the first place bacsue it will not go away once formed.

So all methods that move fluid should have covered pickup and discharge with no bubbles allowed to be sent through the pipes/

Thanks guys, you've been very helpful. We're going to be trying several things, except for the anti-foam agents.

Our maintenance manager is looking into special nozzles as well as experimenting on the inlet pipe placements. The temperature change thing is still unresolved (might cause other problems down the line, I'm told).

About the de-gassing system I mentioned, I inspected one tank and couldn't detect any suction from the duct. The de-gassing fan was running but there seemed to be little or no suction. We took out one section and found that it was clogged. The foam had been sucked in and hardened in the duct, building up over time.

That was strange. With a vacuum, the foam bubbles should have burst as they formed. Instead the foam seems to have survived the vacuum. We're now trying to work out if the vacuum may be insufficient. Seems when we added tanks, no one had bothered to check if we needed to change the fan to a higher capacity.

This should have been one of the first things we checked but somehow got overlooked. Anyway, you guys will be glad to know that this thread has been productive for me. Thanks!

Vulcan, two things you have not mentioned. Does the foaming differ when the pipe discharges deep into liquid or just at beginnig when filling an empty tank. Secondly, is this a batch proces or is production more or less continuous, interupted only when tank is filled and you change ove to other tank?

Perhaps vacuum is the wrong approach. Foam appears as external pressure on liquid is reduced and internal pressure of absorbed gas becomes relativley higher. It sounds like you are dealing with a carbonated liquid and presumably this liquid is packaged to the end user s oit is stil carbonated right up t othe point of actual use. What would be the downside to maintaining positive pressure durign the transfer process?

Please understand, I'm an instrumentation guy trying to understand something that chemical engineers are supposed to know (at least the ones that work in this place).

The foam occurs all the time. Our inlet pipes (we're into the cleaning cycle so I got a peak into the tanks) are facing the wall but not all the way to the bottom, more like 3/4 up the tank wall.

We use a batch process to feed six tanks. The process after that is continuous which feeds three tanks. All these tanks foam but more so for the last three tanks. There could be more to this than what I'm seeing or hearing about. I'm very much constrained about giving too much information unfortunately.

As for the vacuum, we've had it forever. Every factory in our company (even in other countries) have them. I've assumed that they've had enough experience to determine that it is really necessary.

The liquid is naturally carbonated. We remove it and it is not part of the product when used. Using positive pressure would not be practical now. We'd have to make big changes to do that. We also can't be assured that the foaming problem will be solved if we make the changes.

The foam occurs all the time

If none of the previous suggestions work... why not using larger tanks, so they can hold the fluid AND the foam????

why not using larger tanks

Funny you should say that.

Last week, we were discussing what we could do to improve certain things here. One of the things discussed was more tanks (oh brother!). Our process has been growing for the past 13 years with additions and modifications that it has become one of those "there's some space here, so let's just fit it right in". Our tanks are different sizes though they are for the same product and just increase our storage capacity.

So there they were, talking about moving Tank A so that we could squeeze Tank I, J and K in. I'm thinking, "more tanks, more level transmitters, more valves, more maintenance". Now, you got me thinking, "more foam".

Yup, I've got the feeling more tanks will lead to more foam - if you think of the foam being a percentage of the volume of the fluid.

Also, being in manufacturing myself, I'm not to sure the bosses will look too kindly on using up more floor area.

Getting to the root cause and addressing it is the best way to go.

I didn't say MORE, I've said LARGER!!!

sORT OF 3/4 FLUID, 1/4 FOAM

Sorry did you say LAGER?...I'll drink to that...always too much foam in lager.

Not only is my memory going but eyesight as well!

You did say LARGER.

Well, I would take it you mean taller. No can do. Our ceiling height won't allow taller tanks. We are considering replacing some tanks with horizontal ones which will have more capacity than the ones we now have. I pointed out that doing that would not only increase the capacity, but would also mean less items to maintain (One or two large horizontal tank could take the place of six of the tanks). This doesn't actually solve the problem of foaming but the benefits are worth considering.

You did say LARGER

Dear Vulcan... excuse my "glitch" (taller / larger)!

When writing in some other language, I can switch my brain completely into that language, but some conceiled Spanish speaking neurons have probably interfered with the English speaking without noticing it.

Just forget my previous digression (flat discharge to reduce Re). I thought, understandably, that the liquid is beer, so you would want to keep the CO2 in.

Now I get it ! Your problem is to de-gas your liquid while you avoid flooding the building with foam ! Try that:

Right above the liquid maximum level in the tank, install a perforated pipe (pipe diameter larger than the supply) at slight downward angle (3 to 5 deg off level). Discharge your liquid at the end of the pipe through a nozzle at a pressure as high as your distribution system tolerates (the nozzle aligned with your perforated pipe). Hint: the perforation should be about the same size as the bubbles in the foam, not round if you can.

Hey..if the marketing guys were any good....

They'd sell the foam!

The company I am working for is facing similar problem. Can you please suggest me the solution that your company implemented and successfully curbed the foaming problem ?

Hi Anshul Saggar,

I haven't posted in a long time. 'Been busy with other things. We implemented a few things:

We eventually put in more tanks but, instead of using them to maximum capacity, we only fill all the tanks to a little over half-full (vs half-empty ). The foam is still there but it doesn't overflow because it doesn't reach the top of the tanks.

We did lower the temperature of the liquid, which kept the foaming to a minimum.

We also replaced our de-gassing fan with a larger capacity unit.

Now, which one actually solved the problem? I cannot be 100% certain because we implemented all those at the same time (which is typical for companies that get frustrated over a problem so they take out the shotgun and shoot the problem with every solution they come up with ).

regards,

Vulcan

Hi vulcan,

I thought of the following idea.

Laminar flow nozzle or Fontana fountain smooth bore nozzle at the opening of the pipe and bend toward the wall of the reservoir. I hope it works :D .

Anshul

Hi Anshul,

I retired last year and have not asked about the status of this problem. The last I heard was that they rarely experience overflow of foam anymore. They installed a more powerful fan to suck air from inside the tanks. The slight vacuum is enough to burst the bubbles as soon as they are formed. Their new problem is they need to constantly clean the ducts of residue.

By the way, the product is coffee. (",)

regards,

vulcan

Third tank is best to reduce foam generation where the liquid is allowed to tiuch side wall with low speed. ( Pouring beer in glass inclined)