5 replies to this topic

[carbon60]

Hello,

I recently graduated and I am now in change of a pressure filter system. however, we didn't really talk about pressure filters/filtration at all in school so I am having some difficulties making sense of things. My main question is does anyone have any recommendations of books or other resources where I could learn a lot more about them/ mechanism for how filtration works specifically cake filtration.

For the extra helpful that want more details...

I have had experience with pressure filters in the past but now I am trying to vastly improve a process that doesn't really work so well. The thing that is really throwing me for a loop is that I can get really nice flocs in both jar tests and in the tank (Flocs are about the size of the clicker on cheap bic pens, and if left to settle the particles will fall out and leave clean looking water in about 3 minutes) but when I go to filter it the filter blinds very quickly (about 8 gallons/sq foot or 30 minutes of run time) and a wet cake is produced. I am wondering if anyone has any suggestions on what might be causing this. we do not precoat the filter media but we do body feed filter aid and polymer.


Thank you are for your help

[Erwin APRIANDI]

Hi carbon60,

I don't really get the question that you are trying to get from us, is it regarding to the press filter working principle or regarding to flocculant addition to your process fluid. And I really don't understand regarding to this phrase

"The thing that is really throwing me for a loop is that I can get really nice flocs in both jar tests and in the tank (Flocs are about the size of the clicker on cheap bic pens, and if left to settle the particles will fall out and leave clean looking water in about 3 minutes) but when I go to filter it the filter blinds very quickly (about 8 gallons/sq foot or 30 minutes of run time)"

please elaborate further, from my experience with flocculant and press filter is you should be able to get a quite stable and you should also add what kind of press filter type that you are using

is it
1. Chamber Filter
2. Membrane Filter Press
3. Plate & Frame Filter Press

[carbon60]

Hello Erwin and sorry for the confusion.

The type of filter I am using is a single platen pressure filter with a cloth media

I guess really I have three main questions

1) What are some suggested books or other resources where I could learn more about flocculation as it pertains to filter effectiveness. What I want to accomplish here is simply to expand my knowledge of the flocculation process and gain a much deeper and technical understanding.

2) Are there rules of thumb that can direct me when performing Jar tests to guide me on how successful filtration will be. What I am trying to accomplish here is to discover what to look for in jar tests that will translate into good filter results. Should I be looking for large sweep floc, dense small flocs, ect

3)I do not understand why I can get fairly large floc that dropout and leave clear water in Jar tests, but when I go to filter the waste through the filter press the media blinds off quickly, the differential pressure skyrockets, and I get a muddy cake. Is this is symptom of overdosing polymer? For single platen pressure filters should I be trying for smaller denser flocs that may or may not drop out?


Thanks again for the help

[breizh]

Hi ,
Why don't you ask support from the vendor of flocculant ? It should be your advisor ( technical service)

Breizh

[kkala]

...The type of filter I am using is a single platen pressure filter with a cloth media. I guess really I have three main questions
1) What are some suggested books or other resources where I could learn more about flocculation as it pertains to filter effectiveness. What I want to accomplish here is simply to expand my knowledge of the flocculation process and gain a much deeper and technical understanding.
2) Are there rules of thumb that can direct me when performing Jar tests to guide me on how successful filtration will be. What I am trying to accomplish here is to discover what to look for in jar tests that will translate into good filter results. Should I be looking for large sweep floc, dense small flocs, ect
3)I do not understand why I can get fairly large floc that dropout and leave clear water in Jar tests, but when I go to filter the waste through the filter press the media blinds off quickly, the differential pressure skyrockets, and I get a muddy cake. Is this is symptom of overdosing polymer? For single platen pressure filters should I be trying for smaller denser flocs that may or may not drop out?

1. Books on flocculation were thought not common, but a search in www.bookfinder.com indicates the opposite. You could chose one close to your specific application. Suppliers' pamphlets (or web pages) can give useful info, and so can direct contact as suggested by breizh. http://www.wioa.org....vic/paper20.htm indicates that too much flocculant can be either harmful or not. Patient observation of the specific process in operation, along with its parameters can be quite valuable in "feeling" the specific filtration case.
2. Probably the conditions for good filtration depend on the fliltrate & cake quality. In theory coarser particles will create more voids in the cake, so easier filtration. But this is to no avail, if a gelatinous precipitate is created. Filterability can depend on pH, temperature, crystal purity. Not to say also from crystal freshness, observed in alumina plants. Why not try to filter the flocks in the lab, when these are prepared? This could give a clear indication, guiding you to favorable conditions. A Büchner funnel http://en.wikipedia....%BCchner_funnel can be used in the lab, even if it does not represent a pressure filter (http://www.solidliqu...rs/pressure.htm). Of course patient experimental work is needed. This may be supervised here by a flocculant supplier, if a flocculant is to be used. Supplier may direct the research to polyelectrolytes instead of simple substances (e.g. flour, used in alumina plant red mud settling), but time is usually of essence and you can assess an alternative later, when filtration functions satisfactorily.
3. Most of questions were touched above. Conditions in lab may not represent exact plant conditions. You may try to filter a plant sample in the lab, to see what bad filtration means labwise.
Although we had not tried flocculants in filtration, I had heard that flocculant (significant) overdosing could have a negative effect (see para 1 for example). As noted above, it is not only flocculant (or rather lack of it) that can cause harm to a filtration process. Having worked in fertilizers, I observed phosphoric acid disk vacuum filters to retain gypsum (CaSO4*2H2O). Even a small temperature excess over 80 oC in reactor tank destroyed filtration, creating CaSO4. The latter was quite a small percentage of CaSO4*2H2O content in mentioned tank, yet able to create lots of cake full of liquid, needing hours for restoration. During critical field tests, a Director (connoisseur in the field) investigated cake crystalls through a microscope.

Edited by kkala, 13 November 2011 - 09:15 AM.

[Erwin APRIANDI]

Hello Erwin and sorry for the confusion.

The type of filter I am using is a single platen pressure filter with a cloth media

I guess really I have three main questions

1) What are some suggested books or other resources where I could learn more about flocculation as it pertains to filter effectiveness. What I want to accomplish here is simply to expand my knowledge of the flocculation process and gain a much deeper and technical understanding.

2) Are there rules of thumb that can direct me when performing Jar tests to guide me on how successful filtration will be. What I am trying to accomplish here is to discover what to look for in jar tests that will translate into good filter results. Should I be looking for large sweep floc, dense small flocs, ect

3)I do not understand why I can get fairly large floc that dropout and leave clear water in Jar tests, but when I go to filter the waste through the filter press the media blinds off quickly, the differential pressure skyrockets, and I get a muddy cake. Is this is symptom of overdosing polymer? For single platen pressure filters should I be trying for smaller denser flocs that may or may not drop out?


Thanks again for the help

Dear carbon60,

I forgot to ask you the most important point,
What is the subtance that you precipitate with flocculation, is it a stable sendiment
and what is the expected particle diameter? Not all sendiment can be filter press, as filter press required a minimum particle sized due to pore opening in the cloth.

If you apply press filtration for small diamater or solid particle it will not be effective since most of the solid will pass throught the cloth. Since the press filtration is mostly done at high pressure around 7-10 bar.

Flocculation will increases the particle size from submicroscopic microfloc to visible suspended particles, but it is form through a process of slow mixing. And the flock is sometimes soft and will break easily if you apply pressure.

1. For book or recources for flocculation is mostly come from a flocculant manufacture I suggest that you search the name of flocculant manufacture and study regarding to their product from their brochure or catalog. Sometimes they also give more explanation on reaction principle and how to calculate the required amount of flocculant. (I've attach one article that I found from Googling)

2. Rules of thumb for jar test, I think all jar test procedure will be same. Just to write up the solid concentration of initial fluid, what is the concentration and amount of flocculant added and what is the rotation speed. Additional you can also check the operating temp and pressure, pH and etc (refer to APHA 1995)

3. I think it is because the particle size of solid inside the solution is not big enough and the amount of flocculant added is to much.

Fell free to question, if you still have doubt

Attached Files

•  OP-Coagulation.pdf   525.42KB   43 downloads

Edited by erwin.apriandi, 15 November 2011 - 09:47 PM.