Purchas D. Handbook of Filter Media

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Table 7.23 Schumacher ceramic candle filter elements

~..,.

Schumalith 20

homogeneous

granular

Schumacel HTHP

heterogeneous

granular/fibre

Dia-Schumalith

asymmetric

granular/fibre

Dia-Schumalith

Star asymmetric,

fluted granular/fibre

Dia-Brandol

asymmetric

granular/fibre

Dia-Brandol-Star

asymmetric

fluted granular/fibre

Maximum temperature (~

Granule/fibre diameter (lam)

Pore size (lam)

Outer element diameter (mm)

Inner element diameter (mm)

Wall thickness (mm)

Flange diameter (mm)

Flange thickness (mm)

Element length (mm)

Filtration area (m 2)

Weight (kg)

1000

120

1000/1500

0.16/0.26

4.2/6.2

1000

12o/3

30/10

1000/1500

0.16/0.26

4.1/6.2

1000

300/3

100/30

1000/1500

0.16/0.26

4.1/6.2

1000

300/3

100/30

10()0/1500

0.29/0.47

3.3/4.7

180

5oo/1

200/5

1000/1500

0.16/0.26

2.7/4.0

180

5oo/1

200/5

1000/1500

0.26/0.45

2.2/3.2

Coarse Porous Sheets and Tubes 297

The structure of the ceramic foam thus effectively replicates the skeletal or

reticulated form of the polyurethane foam discussed in Section 7.2.2. By

selecting grades of polyurethane foam with pores of appropriate sizes (or

combinations of sizes), and by forming it into the desired shape, a

correspondingly wide variety of ceramic foam products may be produced, such

as is shown in Figure 7.24.

Pore sizes are generally characterized in terms of the number per inch or

centimetre, and can be controlled within the range 3-100 ppi. For example,

there are three standard grades ofFoseco's Sedex filters for cast iron alloys; the 10

ppi grade is for ductile and austenitic irons, the 20 ppi for grey iron and the 30 ppi

for malleable iron. As indicated in Table 7.24, the capacity of these rectangular

blocks depends both on their dimensions and on the alloy being filtered.

Figure 7.24. Examples of 'Stelex'ceramic foam filters for molten metals.

Table 7.24 Capacity of 'Sedex' ceramic foam blocks for filtering molten metal a

Block size Surface Maximum capacity (kg)

(mm) area

(cm 2) Cast iron

Grey iron Spheroidal graphite

Ni Resist/Inmold

35x35x22 12.5 50 25

35x50x22 17.5 70

50x50x22 25 100 50

50x75x22 37.5 150 75

50xlOOx22 50 200 100

75x75x22 56 200 100

100• 100• 100 400 200

a Foseco Ltd.

298

Handbook of Filter Media

An approximate relationship between pore diameter and the number of pores is

provided by Figure 7.25. An indication of air permeability as a function of the

number of pores is given by the pressure drop curves at various face velocities in

Figure 7.26. These figures relate to the ceramic foams produced by the Selee

Corporation (now part of Porvair) from the variety of ceramic materials

summarized in Table 7.25: comments on the applications of these foams are

summarized in Table 7.26.

Average cell-size diameter in microns

--------

) ......... x ',~: X 10 J

tl .,

,~0"

!~ "

= jr"

, _ ~

I!!

Cell diameter vs. pores/inch

Figure 7.25. Relationship between pore diameter and pores per inch in ceramic foam.

150

.~ 40

._= 3.0

2.0

9

o 1.0

= 0.5

r/3

0.4

0.3

0.2

t Air

velocity

I i i i i i i 1 i i i i i I I 1, i I

0.1

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 I00

Pores per inch (PPI) fpm = feet per minute

Figure 7.26. Relationship between pores per inch in ceramic foam and pressure with water flowing at various

velocities.

Table 7.25 Typical properties of ceramic foams a

Phosphate Sintered

bonded alumina

alumina

Cordierite

Mullite Partially Zirconia

stabilized alumina

zirconia

Magnesia

Spinel

Silicon

carbide

Chemical

composition

True density

(g/cm ~)

Chemical

resistance

Max. use

temperature

~ (~

Thermal shock

resistance

Compressive

A120~+

99+%A120~

2 MgO

aluminium 2 AI20

phosphate 5 SiO2

3.9 4 2.5

Poor Very good

acids and bases

143() 165()

(26()()) (3()()())

Fair Fair to good

86 349

(5()6)

(125)

1 Ferrous.

especially iron,

tiltration

strength N/cm 2 (psi) (125)

Bending 35

strength N/cm 2 (psi) (50)

Possible 1 Aluminium

applications tiltration

3 A120~ ZrO2+CaO 6 5% partially MgO

2 Si()2 or MgO stabilized Zr02

or Y20 + 35% AI2() ~

3.2 5.4 5 3.6

MgO

A1203

3.6

Fair Good Very good Very good Very good

in bases

11 ()() 1 54() 1 76() 17()() 165()

(2()()()) (28()()) ( 32()()) ( 31 ()()) (3()()())

Excellent Very good Very good Very good Fair to poor

N/A

2()7 N/A 207 317

(3()()) (3()()) (46())

69 N/A 69 86

( 1 ()()) ( l ()()) ( 125 )

l Automotive l Superalloy l Ferrous 1 Chemical

substrates tiltration tiltration industry

144

(2()9)

(93)

l Automotive

catalyst

substrates -

catalytic

converter and

diesel

particulate

traps

SiC

3.2

Good to

very good

165()

(3()()())

Very good

1 54()

(28(}())

N/A

Very good

to excellenl

N/A

N/A N/A

1 Magnesium 1 High

tiltration surface

area

heaters

Table 7.25

(continued)

Phosphate Sintered

bonded alumina

alumina

Cordierite

Mullite Partially

stabilized

zirconia

Zirconia Magnesia

alumina

Spinel Silicon

carbide

2 Non-ferrous 2 High-melting 2 High

filtration non-ferrous thermal

filtration shock

incl. reactive applications

metals

3 Chemical

industry

filtration

2 Chemical

industry

2 Ferrous 2 Automotive 2 Ferrous

filtration substrates filtration

3 Chemical 3 Magnesium

industry filtration

applications

2 Abrasives

3 High wear

applications

~' Selee Corporation.

Coarse Porous Sheets and Tubes

301

7.5 Porous Carbon

Another range of coarse porous media may be formed either from elemental

carbon, with its high chemical resistance and excellent thermal properties, or

from activated carbon, the microporous structure of which provides

Table 7.26 Comments on applications of various ceramic foams a

Ceramic composition Comments

Phosphate-bonded alumina

and chromia/alumina

Sintered alumina

Cordierite

Mullite

Partially stabilized zirconia

Zirconia-alumina

Magnesia

Spinal (magnesium aluminate)

Silicon carbide

Used principally for the filtration of molten aluminium and its alloys.

Usable to about 1400 ~ C.

Direct bonding of high purity aluminium oxide grains by sintering

results in a lower surface area than in phosphate-bonded material

and low porosity. Very strong and resistant to high temperatures

and chemical attack.

Especially well suited to severe thermal shock at temperatures

below 1093~ thanks to near-zero thermal expansion coefficient.

Thermal expansion coefficient half way between low level of

cordierite and higher expansion of aluminas. Therefore reasonably

good to thermal shock and can be used to much higher temperatures

than cordierite.

An excellent combination of stability and resistance to both high

temperature and thermal shock.

Far more thermally shock-resistant than alumina alone.

Advantages in non-acidic environments requiring a refractory

body.

Compatible with aggressive liquids, e.g. molten magnesium.

Relatively high thermal conductivity and electrical conductivity

making them suitable for heating elements. Hard, highly abrasive

and resistant to most acids and bases.

a Selee Corporation.

Figure 7.27. Balston filter tubes of glass microfibres.

Table Z27

Filter media

Properties of Schumacher carbon filter media f

Filtration Pressure Specific Porosity Density Linear Temperature Bending Bursting Test piece

fineness drop permeability (%) (%) expansion resistance (~ strength

(nominal) (mbar} b (nPm}' coefficient {Pa)

(lamP' ( 1 {}-6.I/K)

Carbo 3

1{}

2{}

3{}

4{}

Schumaka!

Schumas{}rb, AB, AC 5

1{}

2{}

Schumas{}rb AB 6{}

Schumazin 2{}

pressure

(bar

l0 s Pa)

{}. 3 3{}{} 6.29 2 5 1.4 - 2{}{} a, 1 {}{}{}~ 7 60

{}. 5 2{}{} 9.43 3{} 1.35 - 2{}{}. 1 {}{}{} 7 6{}

1.5 8(} 2.34x1{}~ 4{} 1.2 - 2{}{}, 1{}{}{1 6 17

2.5 4{} 4.69• 4{} 1.IS - 2{}{}, l{}{}{} 4 12

3.5 2{} 9.44x1{}~ 4{} 1.1 - 2{}{}, 1{}{}{} 3.5 1{}

1{}.{} 13 2.42x1{}2 4{} 1.1 - 2{}{}. 1{}{}{} ~ 8

- 4{} 6.29• l{} I 6{} {}.7 - 18{} - -

{}.S 2{}{}{} {}.94x 1(} ~ 6{} {}.75 - 18(} S.S 1S

1.{} 33{} 7.6 3 65 {}.75 - 18{} 3.5 12

2.{} lS{} 1.68x1{} ~ 6{} {}.7 - 18{} 2.5 6

- 8 3.1 5 x 1{}2 6{} {}.5 - 15{} - -

2.{}

15{} 1.68x1{} ! 6{} {}.7 - 18{} 2.5 6

" Ambient air, particle counter.

t, Air (a, 25{}m/min.

'" 1 Nanoperm (nPm)={}.l{}l 3 darcy.

d Oxidizing atmosphere.

" Reducing atmosphere.

f Pall Inc/Schumacher.

dimensions

(ram}

i.d./o.d.

070/4{}

07{}/4{}

Ol 2{}/7{}

07{}13()

07{}/4{}

07{}/3{}

07(}/3{}

07{}/3(}

{}7{}/3{}

Coarse Porous Sheets and Tubes

303

exceptionally high surface areas. These two different types of media have very

distinctive properties, as can be seen from examples summarized in Tables 7.2 7

and 7.2 8.

7.6 Glass Fibre Tubes

The final group of media involving inorganic materials is that employing glass. A

distinctive use of the properties of glass microfibres is the range of Balston filter

tubes (now supplied by Parker Hannifin). In essence, as shown in Figure 7.2 7,

Table 7.28 Schumacher range of carbon filter media

Trade name Description

Carbo

Schumakat

Schumasorb

Schumazin

Technically pure carbon and therefore very resistant to chemical reaction.

Not attacked by hydrofluoric acid. Can be utilized over whole pH range 0-14.

Stable in oxidizing atmospheres up to around

200~

and in reducing

atmospheres to about 1000 ~ C.

An open-pored sintered carbon element with low pressure loss, the support body

is impregnated in catalytical substances. Used especially for catalytic reduction

of hydrogen peroxide, e.g. in exhaust from packaging machines.

Consists of highly porous activated carbon, stable over whole pH range 0-14.

Manufactured from chemically impregnated activated carbon. Its special value

is for the removal of hydrazine from steam and water, together with the attend

ant neutralization of ammonia.

Table 7.29 Approximate dimensions of glass microfibre tubes a

Code Outside diameter (mm) Length (mm)

050-05 19 32

050-11 19 57

100-12 38 63

100-25 38 178

150-14 52 152

200-35 65 230

288-80 65 476

250-150 78 752

a Parker Hannifin Inc.

Table 7.30 Retention efficiencies of glass microfibre tubes a

Grade

Gas (retention ofO.1 lam) (%)

Water ( 9 8% retention of particle size) (Bm)

D 93

C 98

B 99.99

A 99.9999+

AA 99.9999+

0.9

0.3

a Parker Hannifin Inc.

304 Handbook of Filter Media

these are a simple form of cartridge, made from borosilicate glass microfibres,

similar to those supplied by Whatman (the former owner of Balston) in its range

of glass filter papers (see Chapter 4). Similar tubes are also produced from fibres of

pure quartz, free of binders.

The borosilicate microfibres are bonded with either organic or inorganic

binders to form tubes in five standard outside diameters (from 19 to 78 mm), with

walls approximately 6 mm thick: lengths, as indicated in Table 7.29, range from

32 to 752 mm. Each is available in five standard grades, the filtration efficiencies

of which are summarized in Table 7.30.

7.7 Selecting Coarse Porous Media

As the chapter's title implies, the media discussed here are not intended for the

finest degrees of filtration, although some of them do achieve quite high filtration

efficiencies. They find their main applications in preliminary filtration steps, or in

the treatment of hot gases or of corrosive liquids.

In fact, temperature and corrosion are the guiding factors in choosing among

these media: if the temperature of gas (or liquid) is above 120~ or so, or if the

liquid (or gas) is at all corrosive, then the likelihood is that metal or ceramic will

be used, rather than plastic, although PTFE materials are capable of resisting

most corrosive liquids, and quite high temperatures.

A particular feature of some of these media is their use in the processing of molten

materials, especially metals (for which ceramic foams are used) and polymers ahead of

their being extruded or blown into film (for which sintered metal media are often used).

For the increasingly important process of cleaning hot dusty gases, the porous

ceramic candle is really the only option available to the plant designer, and the

fibre-based, low-density ceramic materials are developing fast to provide

satisfactory process solutions.

7.8 References

1. L Bergmann (1993) 'The world market for hot-gas media filtration: current

status and state-of-the-art', Gas Cleaning at High Temperatures (ed. R Cliff and J P K

Seville), Blackie, pp. 294-306

2. P Neumann and V Arnhold (1995) 'Sika-R...AS: a new generation of

sintered metal filter elements' Filtech Conference, Filtration Society, pp. 13-23

3. R De Bruyne (1988) 'Novel test method used in the study of sintered metal

fibre filter material', Proceedings of AFS Conference, American Filtration Society,

Ocean City, pp. 657-63

4. H Goeminne, R De Bruyne, J Roos and E Aernoudt (19 74) 'The geometrical

and filtration characteristics of metal fibre filters', Filtration & Separation, 11 (4),

351-5

5. D Gifford and H Wagstaff (1993) 'Retimet metal foam in separation

processes' Filtech Conference, Filtration Society, pp. 346-62

Coarse Porous Sheets and Tubes 305

6. P M Eggerstedt, J F Zievers and E C Zeivers (1993) 'Choose the right ceramic

for filtering hot gases', Chemical Engineering Progress, Jan., 62-8

7. T J Gennrich (1993) 'High temperature ceramic fiber filter bags', Gas

Cleaning at High Temperatures (ed. R Clift and J P K Seville), Blackie, pp. 307-20

8. Y Akitsu, H Masaki and O Kyo (1993) 'Ceramic honeycomb filter for gas

cleaning', Gas Cleaning at High Temperatures (ed. R Cliff and J P K Seville), Blackie,

pp. 321-45

9. J P K Seville, G C Teong and V Sibanda (2000)'Gas cleaning at high

temperatures', Proceedings of World Filtration Congress 8, Brighton, Filtration

Society, Vol. 1, pp. 495-510

10. R Cliff, W Keidel, J P K Seville and C J Withers ( 1989) 'Rigid ceramic media

for filtering hot gases', Filtration & Separation, 26(4), 2 65-71

11. A Startin and G Elliott (2001) 'Treating industrial hot gases with ceramic

filters', Filtration & Separation. 3 8(9 ), 38-40

12. P Hodgson (2002) 'Low density ceramic filters for hot gas filtration'. ].

Filtration Society, 2(2), 2 7-30

13. US Patent (19 77)4,024.056, 17May