FILTRATION TIPS for Filtering with DE/PERLITE/CELLULOSE

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From the desk of LOYALTY CHEMICALS LLC

and remember to ALWAYS use filter aids.

(Please note the below suggestions are just that--suggestions and possible solutions. We cannot be held liable for the use of them, they are only suggestions.)

        POST # 1: POSSIBLE CAUSES AND SOLUTIONS to DE/PERLITE BLEED THRU:  

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㰡n style="font:7.0pt "Times New Roman"">        When you are filtering with DE or perlite you will get initial bleed thru while pre-coating until it circulates a couple of times. It is like one person going thru a doorway.  But, when 10 people try to go thru doorway, it bottlenecks.

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羚nt>      Vertical plate filters are much less forgiving than horizontal plate filter. (Most of my bleed thru or haze issues involve filters with vertical screens. The slightest pressure change messes up vertical plate filters.)

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ﳰan>      Bleed thru issues can be caused by air bubbles in precoat slurry. It is really important that there not be any air bubbles in the precoat slurry or any air bubbles visible in the sight glass when you are precoating. You must purge the system of air prior to filtering. If there are, that is the problem and you have to eliminate them. 

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ﳰan>      A seal or gasket or hole in a screen or something of that nature can be the source of DE/Perlite bleed thru. (A brewer with horizontal screens told me that his source of DE/Perlite bleed thru was solved by ᴣheting down the screens鮥. tightening the gadget that goes down the center of all the screens.)

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ﳰan>      DE/Perlite bleed thru can be caused by not using enough DE/Perlite in the precoat phase of filtering.

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      The inlet pressure (going thru inlet pipe) must be greater than the outlet pressure (going out outlet pipe), or the cake will fall away from screen (i.e. "spaceman" effect.)

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ﳰan>      DE/Perlite bleed thru issues may happen if the DE/Perlite is not evenly distributed on the filter screens during/after precoat phase. (For example, DE/Perlite only covers half the screens-the bottom half on vertical screens.) Solution: You must fill the filter vessel all the way to the top prior to adding the DE/Perlite to the precoat slurry/tank.

   Why this should work:

Let me illustrate by example. You have a sealed silo (like a vertical pressure leaf filter) and you take a hose and start pumping in water mixed with DE/Perlite. When the silo is filled you will have water filled to the top and a layer of DE/Perlite on the bottom (there was no pressure for it to suspend it). (An astronaut only floats in space since there is equal gravity all around.) So, when you fill up a pressure leaf filter (with vertical or horizontal screens) with through put (precoat here) and get it completely pressurized throughout, then you dump the DE/Perlite into the precoat slurry/tank-this liquid will be what is coming and going through the recalculating process-it doesn't matter if there is not much liquid left in the precoat tank, the DE will disperse once it is pumped into the filter.

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     You should have or place an AIR BLEEDER on the top of your pressure filter vessel (if it is a pressure leaf, enclosed vessel). This insures that air gets released, helping eliminate air pockets on the cake. You should talk to the equipment maker or expert about this (we here are not equipment experts). Eliminating air bubbles can help prevent bleed thru.

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      You can test whether or not the filter screens are being properly covered precoat materials (DE, Perlite, Cellulose). Just precoat with HALF the amount of material(s) you normally use. Let it circulate, like always. Then, throw in the 2nd HALF of the precoat materials and if the haze immediately goes up, you know the first precoat did not fully cover all the screens.

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      It "may" be that it is best to mix cellulose powder in with the DE or Perlite you are using as a precoat. Sometimes, the cellulose mixed with a fitler material can create a cemet like coating that is beneficial for the precoat. Sometimes, it doesno, it may be better to start with only cellulose, followed by DE or Perlite or it may be better to mix them as the precoat. You should use the one that works best.

  POST # 2: HOW TO MIX PERLITE (Harborlite) INTO THE SLURRY TANK LIQUID:  

MIXING IN HARBORLITE: Harborlite (perlite) is light and fluffy and thus, in general, is more difficult than diatomaceous earth (DE) to mix into the slurry tank liquid. Yes, the perlite tends to float on the top of the liquid, while DE tends to sink. So, what to do?
Answer:

DE wants to sink to the bottom on the slurry tank. So, the operator will set the agitatorऩrection so as to keep the DE in suspension. i.e. Make the DE bubble up i.e. make the DE stay in suspension, rather than sinking to the bottom via going down the drain.

So, with PERLITE the operator needs to REVERSE the direction of the agitator he had set for DE i.e. For PERLITE, you want the agitator to pull down the perlite into the liquid, not try to keep it up on the top. The agitator needs to be set in such a way as to pull the perlite down into the liquid i.e. pull the perlite into the vortex of the liquid whirlpool i.e. going into a whirlpool vortex (as seen in this picture). So, conclusion: however the agitator was set for DE, you should reverse it for perlite. Further, mixing agitators can move the liquid the way you want it to, per your needs. You should have a discussion with a company that sells mixers so as to get one or learn how best to set the agitator to pull the perlite DOWN when working it into the slurry tank liquid. I would encourage you to talk to a few mixer companies. A few links: http://www.philamixers.com/node/104  http://www.philamixers.com/node/81 http://www.mixerdirect.com/impellers.html

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The perlite is pulled DOWN into the liquid vortex.

          POST # 3: GENERAL DIATOMACEOUS EARTH (DE) USAGE FORMULA

DE PRECOAT:

Precoating is when you put the initial bedding of DE on the filter screens. You circulate the liquid and DE around and around to ⥣oat䨥 filter screens with the DE (prior to 魯feeding䨥 DE and liquid through the filter press). Ideally, if you were filtering beer, you would precoat the DE onto the screens by circulating with 쥡n⥥r until you have built up the intial DE precoat. (If you precoat using non-filtered beer, some 鲴ﲠ﬩ds篵ld hit the screens with the DE precoat and that would not be ideal. But, a lot of operators cannot precoat using finished or 쥡nﲠalready-filtered product.)

Then, when the DE precoat is fully covered the screens, you turn on the spigot of the unfiltered beer and run it through the press with the DE 魯feed�ed into it.

If you have the luxury of having a precoat system: DE Precoat Formula: 10 to 15 pounds per 100 sq. ft. of total filter screen area (front of screen and back of screen would be included in the total filer screen area of a Plate & Frame press).

DE BODYFEED:

In general, you want to use a pound of DE for every pound of solids you are trying to remove. Example: 1,000 gallons of waste water with a 100# of solids in them that you wish to remove via DE filtering. You would need to throw in 100# of DE to filter out the 100# of solids from the 1,000 gallons of waste water.

 

    POST # 4: SOLIDS BLEEDING THROUGH DURING FILTRATION CYCLE

For solids bleed through problem, one thing you want to look at is the spent DE Cake i.e. the DE Cake after the filtration cycle is completed.

Spent DE Cake can offer clues to what the haze problem is. Below, are some things to look at:

 1.     Is the Spent DE Cake smooth? (It should be nice and evenly arrayed across the filter screens/pads.) A smooth and even Spent DE Cake indicates no break in the DE Cake during the filter cycle.

2.     2. Is the Spent DE Cake cracked---any cracks that look like there was an Ჴhquake䵲ing the filtration cycle? If so, that would be an indication of fissure points in the DE Cake where solids would get thru the screen and into the finished product.

3.    3. Does the Spent DE Cake have ﯮ cratersﮠits surface? Moon craters would indicate air pockets/bubbles being introduced during the filtration cycle and this would cause solids to bleed thru into the finished product.

4.     4. Is the Spent DE Cake overly wet and mushy? If so, this possibly may indicate not enough DE is being applied to the screen i.e. You have to add more DE in some wet cake instances.

5.     5. Dark horse theory: The DE Cake, during filtration cycle, is held up via the pressure of the liquid going as it makes its way thru the filter cake and screens. However, but gravity is at work here, too. How? The DE Cake is still pulled down by gravity. In fact, the DE Cake would fall down because of the natural gravitational pull, save for the more powerful pressure of the liquid holding it up (the liquid getting filtered). However, if the pressure of the liquid being filtered is not great enough to hold up the DE Cake, then the cake can fall down. Even if it falls down a little, it would let solids (haze) go thru into the finished product. This phenomenon would be most likely to happen toward the end of the filtration cycle, as the cake gets heavier from the solids it holds (more and more of as the filtration cycle runs).

 

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