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SILICON Diatomite Supercel

It is a mineral of vegetable origin. It represents the accumulation of an enormous number of fossil diatoms. Diatomite is called miraculous mineral because of its lightness, porosity and its uniquely honeycomberd structure which makes it an ideal filtering medium. And because of its inherent stability and the absence of most trace elements, Diatomite is ideal for use by processor who have very high purity requirements such as the food, beverages and pharmaceutical industries, etc.

FILTRATION “THEORY”

Filtration using diatomite is a two step operation. First, a thin protective layer of filter aid, called the precoat, is built up on the filter septum by recirculating a filter aid slurry. After precoating, small amounts of filter aid (body feed) are regularly added to the liquid to be filtered. As filtering progresses, the filter aid, mixed with the suspended solids from the unfiltered liquid, is deposited on the precoat. Thus, a new filtering surface is continuously formed. The minute filter aid particles provide countless microscopic channels which entrap suspended impurities but allow liquid to pass through, without clogging.
 

An efficient, economical filter aid must:

1) have rigid intricately shaped, porous individual particles.
2) form a highly permeable, stable and incompressible cake
3) remove even the finest solids at high rates of flow
4) be chemically inert and essentially insoluble in the liquid being filtered.

In the use of filter aids the ability of the filter aid to remove small particles of suspended matter decreases as the particle size of decreases, and thus the flow rate, increases. Conversely, as filter aid particle size and therefore the flow rate decreases, the ability of the filter aid to remove small particles of suspended, matter increases. The extend to which this takes place will depend very much on the type and particle size distribution of the non soluble solids being removed. In most instances, the particle size range of non soluble solid is such that a fine grade of filter aid, down to the finest will improve clarity. If, however, a given filter aid grade will remove 100% of the suspended solids, a finer grade while giving a lower flow rate due to its finer structure, will not give increased clarity. The selection of the proper filter aid grade is compromise between high clarity and low flow rate, and lower clarity and higher flow rate. The best filter aid is that grade which provides the fastest flow rate while maintaining an acceptable degree of clarity, which must be determined and specified by the filter aid user

For a given liquid, clarity of filtrate is governed by:

Grade and amount of filter aid for body feed - grade and amount of filter aid for precoat - length of cycle and by filtration rate grade and amount of filter aid for body feed - grade and amount of filter aid for precoat - length of cycle and by filtration rate

THE FILTRATION SYSTEM

The essentials of a filter aid filtration system consist of the filter, the filter feed pump, tanks
containing filter aid for precoating and body feed pump for continuous addition of filter aid. Note also the lines for filling the body feed tank and precoat tank with filtered liquid, and circulating clear or filtered liquid containing filter aid between the precoat tank and the filter. The system may also include a precoat circulating pimp and auxiliary lines for blowing back the filter heel to the feed tank, and for filling and recirculating wash liquid, as well as vent lines and lines for blowing the filter cake dry with air, inert gas or steam.Continuous addition of filter aid (body feeding) is accomplished either by feeding filter aid as a slurry or by dry feeding. Slurry feeding is usually done with plunger or diaphragm pumps. If filtration is a batch process, the filter aid can be added directly to the batch as admix. In the operation of a filtration system, the filter is first precoated by circulating a mixture of filter aid and clear or filtered liquid from the precoat tank through the filter and back to the precoat tank. This is continued until all the filter aid is deposited on the filter septum. The body feed injection system is then started and the filter is changed over, with minimum fluctuations in pressure, from precoating to filtering.

PRECOATING

The first step in the use is to built up a “precoat” of filter aid on the filter septum.
The purpose of the precoat is threefold:
1. To prevent the filter septum from becoming clogged by impurities, prolonging septum life.
2. To give immediate clarity.
3. To facilitate cleaning of the septum at the end of the cycle.
Precoating is accomplished by circulating a slurry of filter aid and filtered or clear liquid between the filter and the precoat tank. Since most of the filter aid particles are smaller than the openings in the septum, they must from the precoat by bridging these openings. These bridges can be upset by air bubbles, sudden changes in pressure, or vibrations, causing the filtrate to become turbid until the upsetting influences have been corrected. If flow distribution in the filter is good, the filter may be filled with clear precoat liquid and a concentrated slurry of filter aid may then be pumped or educted into the filter followed by recirculation

AMOUNT OF PRECOAT

The amount of precoat should be from 5 to 10 Kgs. of filter aid per 100sq.ft. of filter area, the greater amount being used when distribution of flow in the filter is poor, or in strating up new filters. If it is perfectly distributed 4.5 kg of filter aid per 100 sq. ft. of filter area will give a precoat of approximately 1.6 mm in thickness. The use of baffles of precoating at a different rate may be necessary for an even precoat at lower precoat amounts. Precoat slurry concerntration will depend primarily on the ratio of filter area to the liquid volume of the filter and piping. If oncentration is much below 0.3% precoating may be difficult since the formation of the bridge depends partly on the “crowding” effect of the particles of trying to get through the septum openings.

PRECOATING RATE

The precoat pumping rate will depend mainly on the viscosity of the liquid used. The rate should be sufficient to keep all the filter aid in suspension but should not be fast enough to cause erosion of precoat in the filter. For water, a typical rate is from 5 to 7 litre. Per sq.ft.of
filter area per minute (gsfm), or 40-80 liters per sq.m.of filter area per minute. For viscous liquids, the rate may be as low 20 liters per sq.m per hour. A general rule for precoating is to precoat at that rate which gives a differential pressure of approximately 2 lbs./sq.in (13.8 kilopascals). For water, an upward velocity of at least 4 ½ ft./min. (1.4 meters/min.) Is equired for proper filter aid suspension. The suspension of filter aid can be improved in the
tank type, or pressure leaf filter, by recirculating part of the inlet flow from the top of the filter back to the precoat tank.

TROUBLESHOOTING

Precoating filtrate should clear up in 2 to 5 minutes. However, this does not mean the recoat is all in place. Continue precoating until the liquid in the filter shell is relatively clear. This usually takes place in 10 to 15 minutes at most. Lack of clarity of filtrate could be caused by any precoat erosion caused by too high a circulation rate; blinding of filter septum; insufficient precoat at top of leaves caused by too little circulation; tears in septum; old screens with worn and/or separated

 

 

 

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Specifications of Diatomite Supercel

Diatomite Supercel is produced by Calcination of material along with flux at 1100 -c to 1200 -c, This produces each coated Particle for clear & Higher rate of flow for filtration.

Spec.
Grade 918
grade 920
Grade 540
Grade 535
Grade 525
Grade Beverages
Colour

White

White

White

White

White

White

Texture
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Specific Gravity
2.35
2.35
2.15
2.15
2.15
2.15
Dry Loose Density gm/cc
0.36 to 0.40
0.20 to 0.40

0.16 to
0.22 to 0.24
0.20 to 0.22
0.16 to 0.18
Water absorption% weight of diatomites supercel
80 to 85
120 to 150
120 to 150
90 to 120
100 to 130
120 to 150
% Water as shipped
0.3
0.3
0.3 to 0.5
0.3 to 0.5
0.3 to 0.5
0.3 to 0.5
Flow rate With h2o at 1kg/Min/sq.mtr pressure
60 to 65
litre
80 to 85
litre
85 to 100
litre
83 to 100
litre
70 to 90
litre
85 to 100
litre
Mesh Size (Air Classified)
200
200
325
325
325
325


Chemical Composition

Spec.

Grade 918

Grade 920

Grade 540

Grade 535

Grade 525

GradeBeverages

SiO2 %
99 to 96
88 to 92
86 to 92
90 to 92
88 to 92
88 to 92
Al2O2%
4 to 7
4 to 7
4 to 7
4 to 7
4 to 7
4 to 7
Fe3O2%
0.35
0.35
0.35
0.35
0.35
0.35
Cao%
Traces

Traces
Traces

Traces
Traces
Traces
Na2O%
Traces
Traces
1.5
1.5
1.5
1.5
K2O%
0.1 to 0.5
0.1 to 0.6
0.1 to 1.5
0.1 to 1.5
0.1 to 1.5
0.1 to 1.
Loose on %
Ignitation at
1000 C
Max 0.5
0.5
0.5
0.5
0.5
0.5
PH
6.5 to 8.0
6.5 to 8.0
6.5 to 8.0
6.5 to 8.0
6.5 to 8.0
6.5 to 8.0

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