Dave Finkelnburg on fri 11 aug 06
Bruce,
No, I don't see any flaws...as long as the process
works as you describe. I do like how you are thinking
about it!
In my experience, filters work this way. The
filter cake is really the filter. When you put the
slurry against the filter dirty water comes through
until a cake is established. Then the cake does the
filtering. The thicker the cake, the slower the
filtering rate. Clay, as you might expect, makes a
poor filter medium.
Good pressing...er...filtering! :-)
Dave Finkelnburg
--- Bruce Girrell wrote:
> Would it not be possible to design a machine that
> does produce a filter cake of relatively uniform
> consistency?
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Bruce Girrell on fri 11 aug 06
OK, so filter presses don't really press...
which begs the question, "why not?".
I am guessing that the answer is that those who use machines of this =
kind are more interested in speed than uniformity.
Would it not be possible to design a machine that does produce a filter =
cake of relatively uniform consistency?
Let's limit the problem to one set of plates and mesh. If the method =
works for one set, then it is easy to make a stack to provide more =
processing capacity. I imagine a set of plates that _would_ be subjected =
to pressure. The interior surface of each plate would have a pattern of =
shallow grooves and through holes. The grooves connect to the holes, =
allowing filtrate to escape from the entire surface area of the mesh.
Set one plate horizontal with the grooved side up (a stack of plates, =
then, would end up being a vertical stack). On top of this is a mesh bag =
with a very coarse weave. The mesh bag would be much like a short paper =
grocery sack. Inside this coarse weave bag is a second bag of a fine =
weave mesh. It, too, is built like a short paper grocery sack, just =
small enough to fit inside the coarse weave bag. With the bags open, =
clay slop would be poured into the inner, fine mesh bag. The top of =
inner bag would be folded over to close in the slop. The top of the bag =
could be shaped suitably to make folding easy and not create too =
overlapping layers. Likewise, the top of the outer bag would then be =
folded over the inner bag. Finally, the upper plate, groove side down, =
is placed on top of the whole affair.
The inner bag is the actual filter bag. The outer bag provides =
mechanical strength and also prevents the fine mesh bag from deforming =
and filling in the grooves of the metal plates. The coarse weave =
provides channels for fluid to flow to the grooves and holes. =20
When pressure is applied to the plates, water should be expressed =
relatively uniformly across the entire face of the plates. Because the =
clay will immediately build up a filter cake limiting the flow of water =
from the clay, there will still be drier clay on the top and bottom with =
wetter clay toward the middle, but it should be fairly easy to determine =
through experiment how much clay could be processed at any one time to =
produce a reasonably uniform density throughout. As stated before, =
increased capacity is provided by increasing the number of modules in =
the stack. To some extent, capacity could also be increased by =
increasing the area of the plates with the limiting factor being the =
ability to deliver pressure over large areas.
Once the water has been expelled, the bags can be opened up, the inner =
bag can be removed from the outer bag and turned inside out to release =
the clay.
Hopefully, I have described the system sufficiently clearly. Anyone see =
any flaws? This is where it would be nice to allow images on Clayart.=20
Bruce "hopelessly an engineer" Girrell
Taylor Hendrix on sat 12 aug 06
I believe you would be getting most of the water expressing from the
edges of your filter bags where no plates obstructed the flow rather
than uniformly across the bag's surface. I'm betting this would cause
problems with plate movement once enough stiff clay packed itself into
the edges of your double bags. I'm also betting that you would have
real problems with blow out at these weak areas. Stronger support
bags might inhibit filtration. I'm just spitballing with you, B, so
this could all be butt-talking.
Your double bag system seems to greatly increase handling time over
the traditional filter press. How will you get the slip into the bags
and how will you get the cakes out? In the standard system, the cakes
just peel out of the freed 'bags' once the clamping on the plates is
released.
On 8/11/06, Bruce Girrell wrote:
> OK, so filter presses don't really press...
>
> which begs the question, "why not?".
...
> Set one plate horizontal with the grooved side up (a stack of plates, then, would end up being a vertical stack). On top of this is a mesh bag with a very coarse weave. The mesh bag would be much like a short paper grocery sack. Inside this coarse weave bag is a second bag of a fine weave mesh. It, too, is built like a short paper grocery sack, just small enough to fit inside the coarse weave bag. With the bags open, clay slop would be poured into the inner, fine mesh bag. The top of inner bag would be folded over to close in the slop. The top of the bag could be shaped suitably to make folding easy and not create too overlapping layers. Likewise, the top of the outer bag would then be folded over the inner bag. Finally, the upper plate, groove side down, is placed on top of the whole affair.
>
> The inner bag is the actual filter bag. The outer bag provides mechanical strength and also prevents the fine mesh bag from deforming and filling in the grooves of the metal plates. The coarse weave provides channels for fluid to flow to the grooves and holes.
>
Ivor and Olive Lewis on sat 12 aug 06
Dear Bruce Girrell,=20
I think this is what Harry Davis shows in his book, a device powered by =
a suction pump. See pp 115-129
Dewatering is needed in many industries. There are devices that produce =
a homogenous product. Feedstock is run from a feed tray over a rotating =
mesh cylinder that has a lower pressure than atmospheric inside. Water =
is sucked from the slurry to leave a film of product. This is skimmed =
from the mesh by a sharp blade. The edges of the blades are hardfaced =
because of the abrasive nature of the product. For more details check =
out the production of Toilet Tissue.
Best regards,Ivor Lewis.
Redhill,
South Australia.
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