I am trying to find a simple way of separating water from a mixture of
finely
divided silica plus calcium sulphate. The material is waste and the
solid part weighs about one tonne per week.

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Request for Question Clarification by haversian-ga on 06 Nov 2002 11:50 PST

Simple?  Leave it out in the sun until the water evaporates.  I assume
you're looking for something a bit more involved than that, yes? 
Could you give us some idea of the type of solution you are looking
for?  What resources do you have available (sun, space, equipment,
money, time, etc.) to implement the solution?  Where are you located?

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Clarification of Question by enkidutwo-ga on 07 Nov 2002 00:32 PST

Location U.K. hence minimum sun. The material is(at present)
discharged from a 4 inch pipe into settling tanks. The ideal solution
would be to discharge from the pipe to a(small) "machine" which splits
the material into reasonably dry solids and reasonably clean water
which can be discharged to waste.It is important that the solid
material can be disposed of on(say) a weekly basis. Space and time are
critical, Reasonable funds available.

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Request for Question Clarification by alienintelligence-ga on 07 Nov 2002 01:15 PST

Hi enkidutwo,

Have you considered an inertial
or centrifugal separating device?

Sieving or dropping through the air 
can  increase evaporation rates.

Heated compression? You could
compress the material into solid
cubes while extracting and 
evaporating the water.

I can elaborate on any of these
processes if they sound useful.

-AI

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Clarification of Question by enkidutwo-ga on 07 Nov 2002 08:13 PST

Hello A I
I like the idea of centrifugal separation. I went along this line some
years ago, dealing with mining machinery companies, but as soon as I
mentioned one tonne per week the interest diminished.
Regards E T

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Request for Question Clarification by alienintelligence-ga on 07 Nov 2002 13:56 PST

Hi enkidutwo

Speaking of solutions...

Is any part of what you
need to separate still in a 
solution state or is it totally
heterogeneous?

When I was thinking of a centrifuge,
I realized that you might have ALOT
of material to go through and I was 
envisioning a large tumbler something
like what a cement truck uses. Except
a cement truck is obviously interested
in maintaining moisture, so in your
case the tumbler would have holes to
allow water to escape and also have air 
injected within to promote evaporation
as the material moves. I don't think
this would be a final operation since
I believe some water will remain in a
capillary state between granules. For
this part heating and compression
might be simpler.

-AI

I refer you to reverse osmosis, which is explained in an answer I
provided here [ https://answers.google.com/answers/main?cmd=threadview&id=99191
]. Note: skip past the optical brightener part.

Is the goal to merely remove the water?  If so, then just add a
quantity of a known dessicant to the total mixture.  The dessicant
will adsorb the water, but then it will contaminate the remaining
solids.  If this is OK with you, perhaps you should give this 
approach a try.

Good Luck!

Hello F W
I think that reverse osmosis would be more applicable to solids in
solution, rather than suspension.
The water to solids ratio is variable but probably in the region of
10-20 :1, therefore the use of a dessicant would seem to be
impractical in view of the expense.
With kind regards.
E T

The first idea that came to me was filtration.  Either gravity or
pressure-assisted, filtration is usually the best was to separate a
solid from a liquid.  However, the finely divided solid you describe
will probably have a strong tendency to "cake" and plug the filter. 
Still, I would at least try filtering some before going to the more
involved solutions.

suggest that you use combination of heat and mechanical pressure. 
That is assuming you don't want both the water and the solids, its
just that you wanted to separate them so when u dispose the solid
waste u save some money as water become extra weight for you to
process.

i.e. in your factory would probably be boilers, just channel the heat
onto a pan that you could unload the waste and let the heat drive off
the water as steam (works better if you have a contained chamber with
negative pressure - this would draw water away faster as a vapor
stage).  at the end of the week its a matter of just disposing solid
waste either on the pan or in a closed chamber box.

Hi enkidutwo,

In the detergent industry, when we are trying to remove water from
solids such as powder detergent we use a technique called freeze
drying. On a plant scale the process is done in what is called spray
drying Vacs.  Since you said you may have some funds available it may
be possible to check out if you can add this system into your line
process. A manufacturer of such an equipment you can contact for
possible input can be found at:

http://www.niroinc.com/html/chemical/cpilots.html

There are various spraying drying techniques some listed below and
more can be found on the above website. You can discuss with various
manufacturers which technique best fit your needs.

"Bowen No. 1 Tower Spray Dryer can remove water at Evaporation rates
to 40 kg/hr" while the P6.3 Spray Dryer at Evaporation rates to 60
kg/hr or the VB-0.3 Vibro-Fluidizer for drying, heating, or cooling
for wet solids and cakes
at evaporation rates to 40 kg/hr."
 
Hope this helps you somewhat.

Toriresa-ga

What I've learned in my college is that porous materials will remain a
certain amount of water no matter how much you apply heat. I've also
learned that the boiling point of liquids lowers as the pressure goes
down. So I suggest to subject the slurry (I suppose it is one) into a
chamber with negative pressure that applies heat to the material.
You might also use a centrifugal filtration equipment (just like what
others said). It can be used in a continuous operation. I dunno if how
much it would cost to process a 1 ton/week of stream.

two more cents, enkidutwo

   The question really is not how, since there are many ways.
   Question is what is economical and what equipment to use.
    
   I guess we do not have enough data to really investigate the case,
   which is, I guess, you are getting comments  only.

   Anyway, the economical solution is to squeeze the water out,
   similar to wine press or cider making press. The properties of
   your suspension may be diferent, and you may have to scale up,
   but such process, combined with sedimentation ponds, will be the low-energy
   solution - therefore a low cost solution.
           
            Happy squeezing..
hedgie

hedgie: squeezing would be the simplest thing to do but AFAIK it will
be operated in batch and with 1 ton/week of stream, this is not
viable.
In fairness though, I'm not familiar with wine press/cider making
press.
I also realized that there isn't much data available here to work
with. I, for myself, don't know how much water is to be remained in
the solids. I still stick with the centrifugal filtration though :)

Hi dacs

           I like the centrifugation idea too, but that is a batch
operation
too. Quite a bit depends on destination of solids and criteria on the
efluent water. This is a job for an enviromental engineer, who can
take whole
system into account.

But what about the Sedimentation ponds ?
       Sedimentation ponds are designed to hold water and allow
sediment to fall to the bottom. After much of the sediment has been
deposited in the pond, the water flows out over a rock-lined spillway
at
       the top of the pond. This pond under construction on a mine in
West Virginia, will drain a large, level portion of a mountaintop
removal mine.
http://www.osmre.gov/ocphoto3.htm

 This reference also mentiones an important word: flocculation
enhanced by an
 additive.

As far as wine presses go, they range from tiny hand-operated machines
to
large automatised steel tanks. As an order of magnitude estimate: the
yearly shipment of california wine is 450 million gallons a year
http://www.wineinstitute.org/communications/statistics/Sales_01.htm ,
 assuming 500 large wineries to make bulk of that and you get over 
500 liters a day. We do not know ratio of water to solids to
proceed...

enkidutwo:

I've come across this pages that might interest you:

http://www.komline.com/Products_Services/Filtration/RotaryVac.html

http://steadfastequipment.com/rotops.htm

http://www.glv.com/divisions/product/download/Rotary_Drum_Filter/GLV_RotaryDrumFilter_Rev.pdf


It's all about rotary vacuum drum filter. It can be operated
continuously and can process from medium to large process stream. But
with no further data to look at (such as water content of the waste),
we can't go further

hedgie: Sedimentation with flocculation/coagulation would be a good
suggestion (provided they can afford to have an ample space to build
the ponds). All we need is gravity (therefore not an energy intensive
process) plus flocculants/coagulants but still, no data from enkidutwo