Understanding filtration:
Cartridges
Part 1
he various types of filtration systems used in
our industry have “come and gone” several times
over the past 70 years. From the heavy canvas covered screens,
to the fine mesh stainless steel, or monel,
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Carbon also has changed its form over the
years from finely-ground activated powder to granules of
activated chips. Although, some of the users of diatomaceous
earth (filter powder) are using the carbon powdazer as part of
the pre-coating process. A comprehensive discussion of
activated carbon will be made later in this series.
During the 1960s and early 1970s the
regenerative powder filter gave way to the much more convenient
cartridge filter. Although the filter powder and activated
carbon powder pre-coat gave excellent results, there were
problems with the pre-coat breaking up to damage the load
together with the sloppy procedure in handling the spent powder
residue from the muck cooker.
This was the result of not
“cooking” the spent powder and carbon, with its
non-volatile residue, completely to include the steam, or air,
sweep to attain a bone dry residue. Also, the filter powder
added more disposable waste which later became a legal issue as
well as being costly to haul away.
The cartridge filter has many advantages
over the older methods of filtration:
1. Convenience
and simplicity.
2. No damage to
garments when expended or under reduced solvent flow.
3. Easy to
store.
4. Can be used
the next day without any procedures.
5. Can be
checked for performance easily by observing gauge or flow
meter.
6. Lower cost
than filter powder.
7. Long life
through use of high performance pump and pre-lint or disc
filter.
8. No purchase
of extra cartridges need be made until the presently used ones
are almost ready to be replaced.
9. After the
activated carbon and carbon/clay combination cartridges are
spent, most of their solvent content can be azeotroped and
“cooked out.”
There are several types of cartridges in
use today with various adsorption materials and also without
adsorption materials (all paper). Cartridges come in three
basic sizes: standard (7" diameter, 14" high), full
size jumbo (13" diameter, 18" high) and jumbo
“split” (13" diameter, 9" high).
All three come with pleated paper only,
and the jumbo cartridges also come with activated carbon
granules in the center or with a combination of activated
carbon granules and heat-treated attapulgite clay.
This last type of cartridge adsorbs the
following in consecutive order (the first being the greatest
adsorbed):
Water
Alcohols
Acids
Aldehydes
Ketones
Olefins
Natural esters
Aromatics
Cyclo-paraffins
Paraffins.
The activated carbon chips adsorb dyes
primarily.
The amount of carbon contained in the
standard size cartridge is 2 pounds, and the total square feet
of filter surface area is 38.6.
The amount of carbon contained in the
all-carbon standard size cartridge is 8 pounds, and this
cartridge is never used for filtering insoluble soil since its
only function is conditioning of the solvent to remove dyes,
essentially, with some other soluble soil also removed.
The amount of carbon contained in the
jumbo full-size cartridge is 16.5 pounds, and the total square
feet of filter surface area is 69.3. The amount of carbon
contained in the jumbo split size cartridge is 8 pounds, and
the total square feet of filter surface area is 34.2.
The jumbo full size, or split size,
cartridge with activated carbon and pleated paper only can
serve as an excellent carbon tower for primary filters of all
paper cartridges or spin disc filters.
Some manufacturers of cleaning machines
offer a special size canister which holds one or two knit bags
of activated carbon granules as a carbon tower for solvent
conditioning only.
The main disadvantage of this knit bag of
carbon is the messy handling of the carbon bag after it has
been spent since it is almost impossible to azeotrope the
solvent out within the still without bursting the bag.
The jumbo full-size adsorption cartridge
contains 8 pounds of activated carbon and 14 pounds of the
extruded and heat-treated attapulgite clay. The jumbo split
size adsorption cartridge contains 4 pounds of activated carbon
and 7 pounds of the extruded and heat-treated attapulgite clay.
Some filter cartridge manufacturers market
these filters as substitutes for distillation, especially for
petroleum solvent users with older transfer units or dry-to-dry
units without a still. However, this author strongly adheres to
distillation to condition solvent in addition to any form of
cartridge filtration.
Composition of a cartridge filter
1. Outer shell (not used by all
manufacturers)
As the solvent flows into the filter
housing, or canister, it strikes the metal perforated outer
shell which protects the pleated paper and also traps large
portions of lint. The number of perforations and their size
must total not less than the aggregate size of the holes in the
paper in order to maintain the proper flow rate of
solvent.
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The flow rates for perchloroethylene are:
3 gallons per minute (gpm) for a standard size cartridge, 2.7
gpm for a jumbo split size cartridge and 5.4 gpm for jumbo full
size cartridge. The flow rates for hydrocarbon/petroleum
solvent are approximately one gpm more than those for
perchloroethylene due to the lighter weight of the
hydrocarbon/petroleum solvent.
The outer shell also gives more overall
strength to the cartridge in addition to keeping excessive
amounts of lint off the paper. The installation of a pre-lint
filter, or centrifugal disc filter, will add much more
filtering life to the paper.
The jumbo full size filter cartridge does
not contain a perforated outer shell. To use this cartridge as
an adsorptive device with activated clay and carbon, the
manufacturers prefer the flow rate of solvent to be somewhat
restricted in order to have the solvent “channel”
over the adsorptive bed.
This permits the soluble soils and
non-volatile residue (NVR) to adhere to the pores of the
adsorptive material.
2. Pleated paper element
The solvent flows next through the pleated
paper element. Each standard size cartridge contains about
5,770 square inches (40 square feet) of pleated paper. The
paper is made by the wet-formation paper-making process, and it
is treated with a phenolic-formaldehyde resin which is applied
to the paper in its uncured form.
Next, the pleating takes place, and,
finally, the resin is cured on the paper in an oven at a high
temperature. The cured resin gives the paper wet strength,
stiffness and rigidity.
The purpose of the pleated paper is to
remove the insoluble soil from the solvent by entrapping these
particles in the small pores of the pleated paper. These pores
are from 30 to 40 microns in diameter. A micron = 39/1,000,000
of an inch.
The insoluble soil particles, which are
suspended in the solvent, are removed by either of the
following three methods:
Mode A: The
pores in the pleated paper gradually become clogged if the
particles are larger than the pores.
Mode B: The
particles are smaller than the pores through which they are
passing, and they are being trapped on the edges.
These insoluble particles are being held
by an electrostatic, or physical, attraction known as
“Vander Waals Forces.”
Vander Waals was a Dutch physicist who
discovered the process of adsorption (by attraction to certain
elements and minerals) which is similar to metal shavings being
attracted to a magnet and filtration by congregation of
materials.
Mode C: One
layer of particles is deposited on the pleated paper, and this
layer is followed by subsequent layers that build up a
thickness (as a cake). The layers serve as a filter within the
filter of small pores with the microscopic openings between the
particles and layers allowing the solvent to pass through.
In the early stages of a new set of
cartridges, a flow rate of one gallon of solvent per pound of
garments per minute, which is ideal for complete removal of
insoluble soil from the garments and from the drum in an
expeditious manner, will prevent the insoluble particles from
quickly congregating on the pleated paper (as in Mode C).
To alleviate this condition, and to cause
the particles to congregate and encounter Vander Waals forces,
it is best to slow down the flow rate of solvent by partially
closing a solvent flow control valve (located at the downstream
side of the filter pump or just before the filter housing or
canisters). This valve should be a good quality gate valve, and
it should be regulated to reduce the flow rate by about 15
percent.
Also, if you have a pre-lint filter
installed before the primary filter, the bag should be removed
from the canister for the first few hundred pounds of cleaning.
When about one pound of inlet pressure has
been created on the filters, the bag can be inserted into the
canister of the pre-lint filter and the solvent flow control
valve can be readjusted for a one gallon of solvent per pound
of garments per minute flow rate.
Initially, the very small (1-10 microns)
insoluble particles not only pass through the pores of the
pleated paper, they congregate, partially, in the very tiny
spaces between the carbon chips of a carbon core, or all
carbon, cartridge. These tiny spaces between the carbon chips
are called "interstices.”
Since the insoluble particles and the
carbon chips are not porous, the blockage of the interstices
will greatly restrict the solvent flow rate. This condition,
therefore, is alleviated by restricting the solvent flow rate
during the first few hundred pounds of cleaning as described in
the previous paragraph. If all paper (carbonless) cartridges
are used, some insoluble particles can redeposit on the
garments being cleaned. Using a high performance curve pump,
capable of pumping up to 60 psi pressure, will greatly extend
the filtration life of the pleated paper after its pores have been clogged with insoluble
soil particles (with the solvent flow control valve wide open).
3. Inner shell
This shell has openings that are
considerably smaller than those in the outer shell. It prevents
the pleated paper from collapsing under the pressure of the
solvent flowing through the continually decreasing diameter of
the pores.
The perforated inner shell also retains
the carbon/clay chips that are stored in that center chamber,
and it provides some support to the carcass of the cartridge.
4. Inner chamber
This chamber contains the carbon, or
carbon/clay, through which the solvent flows. These materials
are not porous, and the solvent has to channel through the
small interstices between the chips.
5. Center tube (outlet)
The filtered and purged solvent finally
exits through the center tube. This tube can be made from a
resin-treated laminated paper or perforated metal, and it is
wrapped with either nylon or polypropylene to prevent any fine
insoluble particles, or dust, from being carried out of the
cartridge and into the cleaning machine’s drum to damage
the load with loose carbon and soil particles.
Additional protection against this
cartridge leakage of fine insoluble particles is with the use
of felt washers, or pads, placed between each cartridge and on
the ends of the first and last cartridge in the filter housing.
The felt pads will adsorb the insoluble particles as the
solvent passes through them. They also serve as an adsorbent
seal between the metal top and bottom cartridge covers of each
cartridge and the end plates of the housing.
Factors on the construction of cartridge
filters
1. The carton,
filter shell and handles must be rugged enough to withstand
shipment, handling and installation without damage.
2. A solid
mechanical seal between the center tube and the shell, which
does not fail and permit leakage when the cartridge is
tightened down under the felt gasket.
3. Solid
spacers to prevent the folds of the filter paper from
collapsing on each other in handling or use.
4. Heavy
weight, resin-impregnated filter paper properly crimped and
cured must be used.
Next month I will discuss activated carbon
and activated clay together with practical applications and
uses of cartridge filtration.
Note: My spotting video, “The Caplan
Method of Stain Removal,” which includes my comprehensive
text and the handy spotting board reference, is available in
English, Korean (video only) and Spanish (video only) from the
Golomb Group, c/o Dennis McCrory, 7664 Plaza Court,
Willowbrook, IL 60521, phone (800) 679-5856. A lecture and
demonstration are presented similar to my classes over the
years at IFI and SDA. This video and text are ideal for
training inexperienced spotters as well as a good review for
experienced spotters.
Also available from the Golomb Group, in
English and Spanish, is my video on step-by-step shirt
finishing which includes my comprehensive text in loose-leaf
form (English only) outlining each procedure for a
single-operator and two-operator cabinet shirt unit using a
cabinet sleever. Proper forming of the collar using heated
collar formers is demonstrated. Each lay is demonstrated for
top quality with very little effort by the operators.
Attractive detailing and packaging of the hangered shirt,
padding, steam pressures and timing are all discussed. A unique
wash formula to give whiter whites, brighter colors and total
removal of grease and body oils is included in the loose-leaf
note book.
Stan Caplan has over 35 years experience
in his own high volume dry-cleaning, laundry and tailoring
plant and two package plants with adjoining coin-operated
laundry and drycleaning. Stan is the former chief instructor at
the International Fabricare Institute, the Southwest
Drycleaners Association and various other trade
association-sponsored schools throughout the US and courses in
Canada, Mexico, South Africa, Singapore and Hong Kong. Stan
offers consulting, training and engineering services in all
areas from customer service area to the boiler room since 1981.
His complete system withtotal quality management will produce
maximum efficiency, economy and product excellent quality. Stan
can be reached at 7341 Amberly Lane, Suite 310, Delray Beach,
FL 33446, phone/fax (561) 496-2548. His e-mail address is stancap100@aol.com.
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