Note: Descriptions are shown in the official language in which they were submitted.
109964~
The present invention relates to a filter element for
use in an ultra filtration unit, which is particularly suitable
for use in an air recirculation plant.
In recent years, there has been a greater public awareness
of the need to preserve the environment and not to contaminate
the air we breathe. In particular, in the mines, conventional
filtration apparatus has been developed to remove airborne dust
particles from the air which is exhausted to the atmosphere so
as to reduce environmental pollution as far as possible. lhe
apparatus for this purpose usually comprises a series of tube-
like filter elements, each normally closed at one end and formed
of cloth, through which the contaminated air is passed. ~he
particles are filtered out as the air passes through the cloth.
Every so often, when a large amount of particles has accumulated
on the cloth, the cloth becomes clogged and the pressure drop
across the filter elements rises substantially. At this point,
the collected dust must be removed, either by backwashing the
filter elements with alr or by physically shaklng them or both.
Such filter elements, made of cloth tubes, will absarb particles
quite effectively when the dust concentration is high and act
as primary filters for cleaning air from an industrial area
to a dust concentration at which it may safely be discharged to
the atmosphere.
In certain specialized applications, it is necessary to
, ~
provide super clean air which is normally considerably cleaner
than the air we normally breathe. Whereas normal city air might
have a dust content of 5.21 mg/1000 cu ft., super clean air may
only have a dust content of .04 mg/1000 cu ft. For example,
super clean air may be required for the ventilation, cooling or
air conditioning of electrical control rooms, laboratories,
precision manufacturing areas, electric motors, and transformers.
Furthermore, air used in some processes for example, in an
.. -1-
1099648
activated sludge sewage plant has to be very clean. Indeed,
by su~er cleaning the air and reducing the dust content to
.04 mg/1000 cu ft., it was found that the diffuser plates in
a sewage plant, which cost almost one million dollars to replace,
last approximately four times as long when super clean air is
employed. There are many other applications in which such
super clean air is either reauired or desira~le and the process
of providing such super clean air has come to be known as
"Ultra Filtration". Known ultra filtration units draw their
intake air directly from the atmosphere.
When ultra filtration first came into use, the filtering
characteristics of conventional tubular filter bags were improved
by coating their inner surfaces with finely ground asbestos
particles. The asbestos particles effectively removed most
of the dust from the air passing through but, unfortunately, the
filter bags became clogged auickly owing to a cake of dust
forming on the asbestos particles. This would lead to a
considerable resistance to the air flow through the filter bags
and a substantial increase in the amount of energy required to
~20 pass the air through the filter plant or, alternatively, reduce
the effectiveness thereof. Unfortunately, because asbestos
clings so tenaciously to the cloth of the filter elements, it was
very difficult to remove by shaking or, indeed, by backwashing
with air. U.S. Patent No. 3,041,808 discloses a filter element
in which a thin deposit of cellulose fibers is provided between
`~ the cloth of the filter bag and the asbestos particles. The
presence of the cellulose fibers acts solely to permit the
asbestos to be removed from the filter bag when it has become
; clogged with the cake of dust formed on its internal surface.
Recently, it has come to light that asbestos is environ-
mentally unacceptable in that it is extremely hazardous to health.
It is therefore an object of the invention to provide a filter
`` 1~9964~
element for use in an ultra filtration unit which does not
require asbestos as a filter aid, but which nonetheless is
capable of providing super clean air suitable for use in such
applications as those mentioned above. It is also an object of
the invention to provide an air recirculation plant capable of
drawing dust-laden air from an industrial working area, cleaning
the air to an acceptable level and returning the air to the
working area.
Accordingly, a first aspect of the present invention
provides an ultra filtration unit comprising an inlet and an
outlet for the flow of gas therethrou~h, a filter element
comprising a tubular wall of cloth napped on its internal
surface and having a layer of filter aid material deposited
thereon so as to penetrate the nap, said filter element having
a hollow interior in communication with said inlet and an
exterior in communication with said outlet such that said gas
flowing through said ultra filtration unit passes through said
cloth wall and said layer of filter aid material to be filtered
thereby.
Preferably, the napped cloth is heavy napped terylene
and the filter aid material consists of cellulose fibers. It
has been found that, by using cellulose fibers with heavy napped
terylene, an extremely efficient ultra filtration filter can be
provided which completely obviates the need for adding asbestos
to the filter element, as was previously required, if ultra
filtration was to be achieved, and which may last a year or more
before it is necessary to replace the filter aid.
A second aspect of the invention provides an air
treatment plant comprising an air treatment plant comprising:
a primary filter for receiving dust-containing air drawn from
a working area, said primary filter being adapted to remove the
majority of dust particles from the air; an ultra filtration
~c~ ~r~:7<7fc ,~o 4r~
~3~
9~648
unit arranged to draw air from said primary filter and reduce
the dust contact still further to an environmentally acceptable
level, said ultra filtration unit including at least one filter
element comprising a tubular wall of cloth napped on its
internal surface and having a layer of filter aid material
deposited thereon so as to penetrate the nap, said filter
element having a hollow interior in communication with said
inlet and an exterior in communication with said outlet such
that said gas flowing through said ultra filtration unit passes
through said cloth wall and said layer of filter aid material
to be filtered thereby and means for returning air from the
ultra filtration unit to said working area.
The invention will now be described in more detail,
by way of example only, with reference to the accompanying
drawings in which:
Figure 1 is a diagrammatic view in side elevation of
an air
; 20
~ -3a-
16~996~8
recirculation plant;
Figure 2 i5 a perspective view of an ultra filtration unit
forming part of the recirculation plant;
Figure 3 is a sectional view of part of the wall of a
filter element of the ultra filtration unit; and
Figure 4 is a diagram showing the drag versus the mass
of dust deposited for various fabrics.
In the air recirculation plant shown in Figure 1, air
from an industrial working area is drawn by means of a fan 2
through an intake pipe 3 and passed to the base 4 of a collector
unit 5. This comprises several banks of fabric tubular filter
elements arranged in vertical arrays. The air flows up from
the base 4 of the collector 5, through the inside of filter
elements and out through their pervious walls. The filtered
; air is collected in a chamber surrounding the filter elements
and exhausted through an air outlet 6. ~very so often the
~ accumulated dust particles are removed from the internal walls
; of the filter elements, either by shaking or by backwashing with
air, and they are collected in hoppers.
20. The intake air from an industrial area might be expected
~: .
to contain dust, for example a silica dust, at a concentration
of~l~g~ain~cu ft. The fabric collector unit-4 wlll operate at
a collection efficiency of 99.5~ which means that its output air
`would have a dqst~concentration of 0.005 grains/cu ft or 11.5 mg/m3.
This dust level is within the environmental standards for
. ~
acceptable ground level concentrations. That is, it would be
environmentally acceptable to dlscharge air having such a dust
concentration into the atmosphere at ground level. Fabric
..
collector units 5 have been previously employed for this purpose,
~30 namely to clean air rom an industrial area sufficiently for it
to be directly discharged into the atmosphere. To this extent
the fabric collector unit 5 is known and will not be described
- --4--
1~9648
in further detail. In Figure l, the air exhausted in the outlet
6 is shown entering a stack 8 through a stack inlet 9 for
emission into the atmosphere. Air having a dust concentration
of 0.005 grains/cu ft. is in no way acceptable for recirculation
to the working area. The air emitted through the stack into the
atmosphere contains valuahle heat energy which is wasted and
which must be replaced when fresh air having a low level of
respirable dust concentration is drawn into the working area.
In Figure l, a secondary air intake 10 is arranged in the
stack 8 above the stack inlet 9. Warm filtered air having a
dust concentration of 11.5 mg/m3 is drawn off through the intake
lO and passed through an ultxa filtration unit 11 by means of
a second fan 12. The ultra filtration unit ll, which is shown
in more detail in Figure 2, also comprises banks of tubular
filter elements 13 arranged in vertical arrays in a similar
manner to the collection unit 5. The air is sucked in from the
top of the filter elements and flows through their pervious
walls into a surrounding chamber. Most of the remaining dust
contained in the air is deposited on the internal walls of the
tubular filter elementsand can be removed from time to time by
shaking or backwashing with air in a similar manner to the
; collection unit 5. For this purpose, the filter banks are
provided with hoppers 15 in a similar manner to the collection
unit 5 and a backwashing duct 16 connects the collection unit
5 and the ultra filtration unit ll. From the chamber surrounding
.
the filter elements, the filtered air flows through an absolute
filter 14 known as a HEPA filter for (High Efficiency Particulate
Aerosols). The HEPA filter is widely accepted as an absolute
filter with guaranteed collection efficiencies as high as
99.97% on 0.3 microns particulates. The use of the HEPA filter
14 downstream of the ultra filtration unit 11 guarantees that
almost any Government standard will be met and that the dust
--5--
9964B
concentration of the air passing through it will be quite
acceptable to breathe~ The air from the HEPA filter 14 is
exhausted by the fan 12 through an outlet 17 into the working
area.
Of course, from the environmental point of view, the
air to be recirculated could be passed directly through the
HEPA filter from the secondary air intake 10. Such air would
have a dust concentration below the TLV* (belo~) and be acceptable to
breathe directly. Ho~ever, the relatively high dust concentration
of the air in the stack (11.5 mgs/m3) would clog the specialized
HEPA filters so quickly that they would need replacing regularly,
probably as often as once per month. HEPA filters use disposable
glass fiber media and the cost of so replacing them would be
prohibitively high. There would be no advantage to be gained
by air recirculation. The object of the ultra filtration unit
therefore is to reduce the dust concentration to an acceptahle
level below the TLV. The air from the ultra filtration unit
has such a low level dust concentration that it does not clog
the HEPA filter, the only purpose of which is to act as a
safety device in the event of failure of the ultra filtration
unit. If this allows too much dust to pass through, dust
particles start to accumulate in the I~EPA filter causing its
: .
drag-to-air flow to-increase. This results in an increased
pressure drop across the ~IEPA filter which can be detected
and used to signal an alarm that the ultra filtration unit 11
is not working effectively.
I An ultra filtration unit, may have a collection
efficiency as high as 99.8~ . This means that for an intake
dust concentration of 11.5 mg/m3, the dust concentration in
the output air would be 0.02 mg/m3. Not only is this concentration
about l/Sth the TLV for silica, it is also at such a level that
the HEPA filter would be unaffected by this air passing through
--6--
* TLV denotes "Threshold Limit Value"
9g648
it, unless, of course, partial failure of the ultra filtration
unit occurred. As mentioned in the introductory part of the
specification, a conventional ultra filtration unit employs
asbestos particles on the inner surface of the filter elements.
The asbe.stos is introduced into the intake air flow when the
unit is initially charged. After a certain period of time, the
dust particles build up and the filter bags become so clogged
that the pressure drop across them rises to such an extent that
only a small volume of air can pass through them per unit time.
At this moment, the asbestos is removed in the manner previously
pointed out. If a cellulose pre-coat is used this is introduced
in the intake air before the asbestos and facilitates the subse-
quent removal of the asbestos. Not only is the use of asbestos
becoming environmentally unacceptable, it is important in the
described recirculation plant to be able to achieve high flow
rates with a maximum time between filter cleaning operations.
The characteristics of the ultra filtration unit 11 will now
be described in more detail.
In order to achieve a high filtration efficiency, there
are a number of conflicting factors which have to be taken into
consideration. Clearly, the volume of air that can be filtered
per unit time depends on the flow rate through the filter elements.
The flow rate will be greater the lower the resistance to flow
for a given pressure drop across the filter element. ~owever,
generàlly, a low resistance to air flow means that the cloth
must be coarsely woven and a small amount of filter aid material
must be coated thereon. This in turn means that too many
particles will pass through the filter bag and there will be
a relatively low filtration efficiency. On the other hand, a
high filtration efficiency can be achieved by using a finely
woven cloth with a substantial amount of filtered materiai.
Of course, this means that either the flow rate will be reduced
~09964B
or, alternatively, the pressure drop must be increased. In
either case, this will require the expenditure of more energy
to filter the same amount of air. The pressure drop ~p across
a filter bag is given approximately by the expression:
~p = KLTV
7000
where K is a constant dependent upon the properties of the
filter element and the dust being filtered and is known as the
K factor or specific resistivity constant
L is the amount of dust collected in the filter element in grains/
cu ft.
T is the time in seconds, and
V is the velocity of the air flow in feet per minute.
Generally, cloths which provide a good ultra filtration
,
collection efficiency, that is they remove a very high percentage
of air-borne particles, have high K factors. Conseauently, in
; order to maintain an adequate flow across them, they reauire
the expenditure of a considerable amount of energy owing to the
high pressure drop across them and this results in an increase
n the operating cost. With an asbestos coated filter bag, the
~20- filter drag rises to such a~value, after a period of for example,
three~ or four months, that the pressure drop ~p across the filter
element is so high and the air flow through the filter element so "
low that~aIl the filter aid~matérial must be removed and the
filtér~elements have to be recoated.
The drag through a conventional asbestos coated filter
element can be reduced by simply eliminating the asbestos. It
has been found that the cellulose pre-coat, which is primarily
intended to allow the asbestos to be easily removed during
backwashing, does provide some degree of filtration. However,
the filtration efficiency is not high enough for use in the
recirculation plant shown in Figure 1.
In the ultra filtration plant shown in Figs. 1 and -2, the
-8-
9964~
filter elements are made of a coarsely woven terylene cloth
which has been heavily napped on one surface. As is ~ell known,
napping is a process whereby the individual fibers are raised
from the threads of a woven fabric by brushing the woven fabric.
For example, a blanket is a good example of a napped cloth.
Only a single coat of cellulose filter aid, preferably SOLKA-FLOC
(a trade mark) BW 40 is then deposited on the coarsely woven
napped cloth by introducing it into the air intake when the unit
is first charged. As shown in Fig. 3 which is a section through
a part of the wall of one of the filter elements, t~e material
comprises a coarsely woven layer 18 of terylene fabric. The
terylene has been napped on one surface to provide a nap 19
consisting of small individual fibers projectina from the main
cloth layer 18. In use, the cellulose filter aid is deposited on
the inner surface of the filter elements, i.e. that provided with
the nap 19, and, as shown in Fig. 3, the cellulose 20 becomes
entrapped in the fibers of the nap. A thin layer (not shown)
of filter aid may also form on top of the nap 19, although most
; of the filter aid~penetrates within the nap. In use, it has
20 been found that the combination of the nap 19 and cellulose filter
aid material 20 gives an extremely good ultra filtration
efficiency, that is virtually all air-borne particles are removed
from the filtered air, while at the same tlme having a relatively
low K factor. This means that, for the expenditure of a minimum
amount of energy, a high flow rate through the filter can be
achieved at a high collection efficiency. In addition, unlike
previous filters, the filter elements do not tend to clog quickly
and, indeed, have a lifetime between recoating operations
approximately four timeS greater than was the case with an asbestos
filter aid . Of course, these advantages are auite separate from
the environmental desirability of eliminating the use of asbestos
Which is extremely hazardous to health.
1~99648
l~hen, finally, o~ing to the filterelements becoming
clogged, the pressure drop across them increases to such an
extent that it is no longer economically feasible to continue
operation, it has proved to be a relatively simple matter to
remove the filter aid material from the napped cloth. They can
be shaken if desired, although it has heen found that the filter
aid material can be readily removed by simply back~ashing the
elements, i.e. simply by reversing the air flow through them.
This reverse air flow removes the cellu]ose filter aid from the
nap, together with the collected dust particles, and deposits
- it in the hopper 15 of the unit 11. The spént filter aid -
material and dust can then be removed through an opening
in the lower part of the housing. Of course, if desired, the
spent filter aid material also can be removed by agitation.
By way of illustration, reference will be made to Figure 4.
Air was passed through a tubular filter element having an active
surface area of 17.89 sq ft. Various amounts of BW40 SOLKA-FLOC
(a trade mark) filter aid were introduced into the intake air and
;~ ~ deposited on the internal wall of the element.' Figure 4 shows the
~ 20 filter drag plotted against the amount of added filter aid
; ~
material for various fabrics. The drag is measured in terms
of the ratlo of the pressure drop ~p across the bags to the
~- velocity;V of the air flowing through the bags. The add on mass is
the amount of filter aid carried by the bags at the time the
- : :
measurement is taken. Line 1 represents a Barrday style 0049
,
cotton fabric having various amounts of filter aid deposited
on its~ surface. Line 2 represénts a Barrday style 3053 spun
polyester fabric with various~masses of a filter aid. Line 3
represents a style 3503 spun polyester fabric. Line 4 represents
a style 4054 spun polypropylene fabric with a filter ald deposited
on its surface, and line 5 represents a heavy napped terylene
polyester fabric (Barrdày style 3501)*. From the diagram, it can
--10--
* Line 6 represents a style 0049 fabric with asbestos.
1~9964~
be seen ~uite readily that the drag produced by the heavy napped
terylene polyester fabric is substantially less than that of the
other fabrics, particularly cotton with asbestos which is
conventionally used for ultra filtration elements. This reduced
drag enables the great saving in energy, and therefore cost, to
be achieved.
The efficiency of dust collection of the style 3501 heavy
..
nap terylene fabric was compared with a cotton fabric (style 0049)
having an asbestos filter aid. This was carried out by passing
known quantities of test dust m'xed in a feding hopper through
individual filter bags at a constant rate and the total discharge
was monitored by passing the discharged air through a high volume
sample membrane. Any dust passing through the filter is collected
on this membrane which is weighed before and after the test.
The cotton fabric had a collection efficiency of 99.9971 whereas
the heavy nap terylene filter aid had an efficiency of 99.9935
which is quite acceptable. However, the much lower drag of the
3501 fabric compared to the 0049 means that economically, great
savings can be achieved and a much larger volume of air can be
filtered in the same amount of time with the consumption of
less energy.~ The full test results for the two fabrics are
set out below: ~ ~
FABRIC UNDER STUDY: Barrday 3501 (H.N.T.) -B1~40 Filter Aid
TEST DUST: Minex 7 (Mean particle size 5 microns)
Nepheline Syenite
FILTER BAG STYLE: 5" x 168" Strap top
FILTRATION EFFICIENCY EVALUATION
FILTRATION TIME: 53 minutes
TOTAL GAS FILTERED: 53 x 10 x 17.89 = 9482 ft3
TOTAL PARTICULATE F~ED TO THE FEED HOPPER: 18,550 grains
ISOLATED CELL DUST LOADING: Assume 20% of feed rate
FILTRATION VELOCITY (A/C ratio) FOR ISOLATED CELL - 10 Ft.P.M.
~XIMUM DIFFERENTIAL PRESSURE ACROSS FILTER BAG (Dust-on-Fabric)
= 4.9" water gauge (w.g.)
--11--
1~9~64~
MINIMUM DIFFERENTIAL PRESSURE ACROSS YILTER BAG (Dust-on-Fabric)
= 0.7" ~.g.
NUMBER OF CYCLES: one
FINAL CYCLE ADD-ON DUST (i.e. ~ilter aid dust adhering to filter
after completion of test) = Est. .07~/ft filter aid +
0.03 #/ft2 dust = 0.1 lbs/ft2
ESTIMArrED ADD-ON-DUST FOR RUN: 0.3 #/ft fabric
SAMPLER FILTER l^~EIGHT (A~TER RUN) - 4.2783 grams
SAMPLER FILTF,R WEIGHT (BEFO~E RUN) - 4.2628 grams
COLLECTED MASS ON SAMPLF.R FILTER - 0.0155 grams = .2392 grains)
COLLECTION EFFICIENCY: Based on 20% feed rate = 99.9935%
Based on 40% feed rate = 99.9968%
:~
PENETRATION: For 20% feed rate = .000065
For 40% eed rate = .000032
_____________ ~
FABRIC UNDER STUDY: Barrday 0049 (Cotton) - Asbestos Filter aid
TEST DUST: Minex 7 Nepheline Syenite
; FILTER BAG STYLE: 5" x 168" strap top
CLEANING MODE & CYCLE: none
~ FILTRAmION EFFICIENCY EVALUAmION
20 - FILTRATION TIME: 33 minutes
TO~TAL GAS~FILTERED~ 33 x 10 x~17.89 = 5904 ft
TOTAL PA~RTICULATE FEÉD TO TME FEED HOPPER: 11,550 grains
ISOLATED CELL DUST LOADING: Assume 20~ of feed
FILTRATION VELOCITY ~A/C RATIO~ For Isolated Cell - 10 Ft.P.M.
MAXI~1UM DIFFERENTIAL PRESSURE~(Dust-on-Fabric) - 5.2" w.g.
~; MINIMUM DIFFERENTIAL PRESSURE (Dust-on-Fabric) - 1.4" w.g.
NUMBER OF CYCLES: ~ one ~ ~
FINAL CYCLE ADD-ON-DUST - ESt. .06 # /ft2 Filter Aid ~ . 013 #/ft2
2 dust
ESTIMATED ADD-ON-DUST FOR RUN - .019 #/ft fabric
SAMPLER FILTER WEIGHT (AFTER RUN) - 4.2501 grams
SAMPLER FILTER WEIGHT (BEFORE RUN) - 4.2458 grams
COLLECTED MASS ON SAMPLER FILTER - .0043 grams = (.0664 grains)
-12-
9964~
COLLECTION EFFICIENCY: based on 20% feed rate = 99.9971
based on 40% feed rate = 99.9985%
PENETRATION: for 20% feed rate - .000029
for 40~ feed rate - .000015
________________
FABRIC UNDER STUDY: Barrday 0049 (Cotton) - B~40 Filter Aid
TEST DUST: Minex 7 Nepheline Syenite
FILTER BAG STYLE: 5" x 168" Strap Top
CLEANING MODE & CYCLE: none
FILTRATION EFFICIENCY E~7ALUATION (Residual Established)
FILTRATION TIME: - 38 minutes
TOTAL GAS FILTERED: 38 x 10 x 17.98 = 6798 ft
TOTAL PARTICULATE FEED TO THE FEED HOPPER: 1.96 Gr/ft = 13,300
ISOLATED CELL DUST LOADING: Assume 20% of feed
FILTRATION VELOCITY (A/C RATIO) For Isolated Cell - 10 Ft.P.M.
MAXIMUM DIFFERENTIAL PRESSURE ACROSS FILTER BAG ~Dust-on-fabric)
5.5" l4.g.
MINIMUM DIFFERENTIAL PRESSURE ACROSS FILTER BAG (Dust-on-fabric)
1.7" w.~. -
NU~ER OF CYCLES - one
: FINAL CYCLE ADD-ON-~UST - Est .06 #/ft Filter Aid ~ .021 #/ft dust
~, ~
ESTIMATED ADD-ON-DUST FOR RUN - .021 # /ft2 fabric !,
: SAMPLER FILTER WEIGHT (AFTER RUN) - 4.2848 grams
SAMPLER FILTER WEIGHT ;(~EPORE RUN) - 4.2826 grams
. COLLECTED MASS ON SAMPLER FILTER - .0022 grams = .034 grains
COLLECTION EFFICIENCY - based on 20% feed rate = 99.9937%
-`based on 40% feed rate - 99.9393% .
PENETRATION: ~ For 20% feed rate = .000013
For 40% feed rate = .000007
. . .
--__--___ _____ __________
``- Thus, the preferred form of the invention uses a heavy
napped terylene fabric ~Barrday style 3501) with a BW40 SOLKA-FLOC
filter aid at a mass deposit of approximately . 07 lbs of filter
aid per square foot of fabric. This has a high collection
.. -13- ~ -
,
'
.
996~8
,
efficiency and low filter drag. However, a fahric cther than
heavy napped terylene can be used, provided it is napped and
re]atively coarsely woven. The filter aid is preferably
cellulose, but other suitahe aids may be used provided they
are of such a nature that they will become em~edded in the nap
of the fabxic. In effect, the nap means that a coarser fabric
can be used for ultra filtration than would otherwise be the
case. The fibers of the nap form a fine bed which holds the
filter aid material over a relatively thick layer, instead of
allowing it to be compacted against the cloth as is the case
; with an unnapped fabric. Thus, the active part of the filter
has a relatively open structure and the resistance to air flow is
quite low. Nonetheless, because of its thickness, the statistical
chances of a particle of dust passing through the filter striking
a particle of filter aid material are very high and this, it
is believed, is the reason for the coated nap filter having a
high efficiency.
A fllter element made as ~escribed from heavy napped terylene
is extremely effective in the described air recirculation plant.
; 20 The energy requirements for the ultra filtration unit are
sufficiently low for the recirculation of air to be rendered `
highly economical. Furthermore, the collection efficiency of
heavy napped terylene with SOKA-FLOC (a trade mark) filter aid
(99.99%) is more than adequate to provide a dust concentration
: -
which lS below the TLV when fed with air from the primary collection
unit 5.
- .
s
Brown Company, SOLKA-FLOC (a trade mark) filtex aid # BW 40-
has the following characteristics:
colour - white
brightness - 81
! '
approximate average length (microns) 80
approximate average thicknèss (microns) 16
-14-
`` 1~9~648
approximate screen analysis % on 40 mesh: 0.8-1 -,
% through 100 mesh: 83-90 :_
~ through 200 mesh: 25 ~:-
filter cake density (lbs/cu ft) - 11-13 ~'~
approximate moisture (%) 5-7
Iron (~) .0150
Lignin (%3 0.2-0.4 ;-`-
Sulphur (%) .0060
~ Ether solubles (%) 0.2
Copper (%) .0006
Viscosity (cps) 18 ~
Pentosans (%) 2.4 ~ ';
Barrday style S-3501 fabric has the following
_.
characteristics:
T~ARP - SPUN 2 RUN (Wollen System)
FILL - SPUN 2 RUN (Wollen System)
COUNT 3 8 x 27
WEIGHT 14; oz.~-per sa. ~d. ~:~
; PE~ME.ABILITY~50-60 ft3/min~ at l/2" w.g. ,.
~:20 WÉAVE 2 x 2 twill ~ . ~ .
$
. ~ ; FINISN - ~HEAVY NAP (to the dust). :~
.
` ' . ' : .,
~, ' ~
. -15- ;
~'
- ' , " '
