Design of a stirrer 2

[ajxxx]

I would like to know the recommendations of which design amongst the attached would be the best for :

** Creating a VORTEX and highest downward thrust (for pushing the fluid down towards a drain plug) when used as a stirrer...

I would like to know if there are any better designs than the ones I have thought of for achieving my purpose. Thanks in advance

 

[ajxxx]

I have water with polymer in it and CO2 is purged @ 600 psi + "so called mixture" is heated to 150 C and saturated for 1 hour.

Water is both heat sink & transport agent - favoured for use because of cost and no chemical reactions.

No i cannot lower the temp. as the polymer melts @ 150 C...once it melts it absorbs the gas and becomes unstable...once vented to the atmosphere the pressure differential causes it to expand. Polymer achieves "fluidity" @ 150 so it helps in coming out easily with water.

Would metering valves or say a spiral tube @ the bottom port enable me to add more resistance to control the release and also help me provide more resistance to water flow?

 

[EngineerTex]

Call me crazy, but it seems that with the system you have here, you're trying to make it overly complicated. Instead of trying to push the polymer down through the water and get it out through the hole in the bottom of the tank, try this: Put a tube inside the tank with the bottom connected to the bulkhead in the bottom of the tank and have the top end of the open tube a few inches from the top of the tank. Then you just pump water into the tank so that all of the polymer comes out through the tube. You would need a second hole in the bottom so that you can drain the water after you're done.

If the way I explained it didn't make any sense, open a toilet tank and have a look at the overflow tube.

And now that I think about it, at that pressure and temperature, you can simply put a valve on the bottom and let it flow on its own without having to pump anything into it.

Engineering is not the science behind building. It is the science behind not building.

 

[rb1957]

ET,
i don't think he's trying to push the ploymer through the water, but rather trying to separate the water (drive it to the bottom of the receiving tank) and the polymer (drive it to the top of the tank).

it sounds like the water and the polymer mix (at 600psi and 150C). but i'm confused by "the polymer melts @ 150 C...once it melts it absorbs the gas and becomes unstable".

i also have difficulty with venting to atmoshpere a vessel at 150C and 600psi containing a water mixture. this isn't my speciality but isn't the water superheated ? won't it (does it ?) flash to steam ?? won't the 600psi drive the mixture out the vent (something like an enema) ?

is the polymer mixed in with the water ? evenly distributed or globby ??

 

[rb1957]

a random thought ... i've been thinking about the mixture in the receiving vessel ... maybe you're looking for something to help get the mixture out of the oven ? (if you make a vortex the fluid flows much quicker out of the outlet) ... maybe you should create a circulation inside the oven ??

 

[ajxxx]

No infact it is the other way around...water should be pushed up and polymer down(polymer is more lighter)...based on the water table though water density @ 150 C & 600 psi would be 0.91 ----almost equal to that of the polymer melt.

Polymer is evenly distributed in water (agglomeration is prevented by use of talc / surfactant).

Water is used as a transport agent "to" the valve where it is discharged...after discharge water is not important but is critical before that to help drive the polymer to the exit (besides also helping as a dispersing agent during saturation which generates heat due to exothermic polymerization process).

Polymer & Water are "Immisscible" - polymer does not dissolve in water....just floats around and based on water table @ higher temp. evenly "moves" with water (not @ top as densities become same)...

Maybe just my communication is bad as probably I am not being able to explain it properly .....this process is termed "Pre-expansion Of Polypropylene beads (EPP)" in an autoclave.

 

[rb1957]

so the polymer is floating on top of the water ... i'd try a flexible hose, with the end floating at the water interface, sucking the polymer out ...

 

[btrueblood]

Why not just put the hole in the top, or near the top, of the tank?

 

[rb1957]

i googled EPP ad got a whole host of hits ... there's a well established indutry/technology out there (KURTZ seems to be prominent). i doubt that a bunch a guys dispensing free advice will get you where you want to go. i can't suggest that you infringe on someone else's copyright, so i won't !

 

[berkshire]

Think of this as mixing salad oil and vinegar.
If you let it sit, the oil will float on the vinegar.
When you shake it up well, the two will mix temporarily.
ajxxx wants to get the mixture out of the vessel while it is still mixed up.
B.E.

 

[btrueblood]

No, he wants the polymer to come out without the rush of steam/hot water. The polymer will have absorbed water/steam and CO2 under pressure, and these absorbed materials cause the pellets to expand. The external, un-absorbed water just flashes/splashes away and presumably causes trouble.

At least that was my read.

And thus my suggestion to pull the pellets off the top of the kettle, where they are floating...

 

[EngineerTex]

water is secondary : If it comes out after the material = NO ISSUES

I must be missing something here. I will admit that I had trouble with the file that he uploaded (100% a problem on my end) but either way, I must be failing to grasp what the problem is if he can't have a standpipe in the vessel, where he pumps more water into the bottom to force the polymer out through the tube. Or perhaps trying the floating tube as rb1957 suggested.

What I had said before is that you would have the end of the tube a few inches below the top of the vessel, but this would be wrong. My thinking is that if you are making this in batches, you determine where the height of the water-polymer interface will be and set the end of the tube to be at exactly this height. Each batch, you add (ECACTLY) enough water to cover - JUST BARELY - the end of the pipe, then you add however much polymer you need for the batch and the space above the polymer will be filled with steam.

When you open your valve at the bottom of the tank, the polymer is pushed out until you get steam throttling through the valve. To maximize the amount of polymer coming out, you might try having a funnel shape on the upper end of the inner standpipe, up to almost the full diameter of the inside of the tank.

If that wouldn't work, then I have to say that I have no idea what's going on.

Engineering is not the science behind building. It is the science behind not building.

 

[btrueblood]

The problem with a standpipe, or a floating hose, or whatever, i.e. an opening anywhere but at the top of the tank -- is that, as you deplete the polymer load, you must make up the missing space, presumably as ETex says, by adding water. But, this means that the water level must rise to make up the volume left by the polymer that has been removed. At some point, the water level will rise above a standpipe, and all that comes out is steam, with some amount of remaining polymer floating in the top of the tank. If a floating hose, then the volume might be smaller, but there will still be some residual.

A single hole in the top of the tank seems to be the way to go. Or else I have no idea what's going on either.

 

[rb1957]

i'd've thought that the pressure would drop slightly (less stuff filling the same volume) as the polymer is removed.

but like i said, people have examined this problem in detail and arrived at workable solutions, after investing way more effort and thought than we're likely to put in. And i'd expect that all the ideas we're "pop-corning" have been considered already and incorporated or rejected.

just my 2c ...

 

[amainville]

Is the water necessary to the reaction? As I understand the problem statement it is being used as a conductor within the tank. Could you change from that to another material maybe something solid which you could strain out as the polymer exits the tank?

 

[MikeHalloran]

I think btrueblood's got it right; move the gravity vector instead of fighting it.



Mike Halloran
Pembroke Pines, FL, USA