Note: Descriptions are shown in the official language in which they were submitted.
CA 02310740 2000-06-06
C6541 (V)
METHOD FOR CLEANING
CONTAMINANTS FROM EQUIPMENT
FIELD OF THE INVENTION
This invention relates to a superior method for cleaning contaminants from
equipment. More particularly, the invention is directed to the removal of
contaminants
from the internal portions of equipment with a cleaning foam. The superior
method of
this invention allows for the cleaning of internal portions of equipment
without the need
to disassemble any parts. Moreover, the invention allows for the cleaning of
contaminants from the internal portions of equipment, while at the same time,
minimizing the production of environmentally unfriendly waste.
BACKGROUND OF THE INVENTION
The deposition of contaminants in equipment such as boilers, cooling towers,
food and beverage equipment, and pulp and paper processing equipment, can be
detrimental to the efficiency of the various processes being conducted in the
equipment. Moreover, the desired products generated from contaminated
equipment
typically display properties and characteristics that are inferior to products
made in a
contaminant-free environment.
In the pulp and paper industries, for example, internal components of
equipment, such as equipment used in the Kraft process, are subjected to
various
inorganics as part of the processing steps to convert wood chips into pulp.
During the
Kraft process, wood chips are cooked and washed to produce a black liquor that
is later
subjected to evaporation and burning. The resulting product (green liquor) is
subjected
to inorganics like sodium carbonate and sodium sulfide wherein the sodium
carbonate is
CA 02310740 2000-06-06
C6541 (V)
causticized and converted to sodium hydroxide. The causticizing of sodium
carbonate
inevitably results in by-products (e.g., inorganic contaminants), like calcium
carbonate,
that deposit within the processing equipment used to conduct the Kraft
process. Such
contaminants often accumulate within the processing equipment and must be
removed
in order to effectively perform the pulp generation process, preserve the
longevity of
the equipment and maintain the industry demanded quality of the desired pulp
product
being recovered.
Conventional methods for cleaning internal portions of equipment, such as
those
described above, typically employ high volumes of solution that dissolve the
contaminants within the equipment. The solution method, however, has many
disadvantages, including the generation of excess environmentally unfriendly
waste that
typically has to be removed to off-site hazardous waste plants. Also, the
solution
method typically results in the incomplete removal of contaminants from
equipment,
and particularly, those found in the tubing or pipes of the equipment as a
result of
insufficient contact between the tubing or pipe interior walls and the
solution. The
insufficient contact in the solution method is difficult to avoid because
space between
the solution and the interior walls of the equipment (often created by a
pressure relief
mechanism) is needed to prevent resulting by-product gases, like carbon
dioxide, from
rupturing of the equipment being cleaned.
Other conventional methods for removing contaminants from the internal
portions of equipment include the use of high pressure water blasting. Such a
water
blasting method, unfortunately, requires the expensive and labor-intensive
steps of
disconnecting the parts of the equipment prior to cleaning.
It is of increasing interest to develop a method that allows for the cleaning
of
internal portions of equipment without generating excessive environmentally
unfriendly
waste and without the need to disassemble the equipment prior to cleaning.
This
2
CA 02310740 2000-06-06
C6541 (V)
invention, therefore, is directed to a superior method for cleaning the
internal portions
of equipment. The invention employs a cleaning foam that is circulated
throughout the
equipment being cleaned. The invention, unexpectedly results in internal
portions of
equipment that are substantially free of contaminants, does not generate
excess
environmentally unfriendly wastes and does not require the disassembling of
equipment
prior to cleaning. Moreover, the invention unexpectedly results in internal
portions of
equipment that are substantially free of contaminants without the need for
building
pressure relief mechanisms into the equipment. Still further, the invention
utilizes at
least about 50% less, and preferably , at least about 80% less fluids than
conventional
methods used to decontaminate equipment of similar size thereby minimizing the
need
to remove waste to off-site hazardous waste plants.
BACKGROUND REFERENCES
Efforts have been disclosed for inhibiting contaminant deposition in
papermaking
systems. In U.S. Patent No. 5,885,419, the deposition of organic contaminants
in a
paper making system is minimized by adding albumins, globulins and spray-dried
animal
cells to the pulp, or by spraying deposition prone surfaces of the paper
making system
with the same.
Other efforts have been disclosed that convert inorganic materials in Kraft
pulping liquor into pulping chemicals. In U.S. Patent No. 5,034,094, pulp
recovery is
increased by separating organics and inorganics wherein the former is recycled
to a
process loop and the latter is converted into pulping chemicals without the
need of a
recovery furnace.
3
CA 02310740 2000-06-06
C6541 (V~
SUMMARY OF THE INVENTION
The present invention is directed to a superior method for cleaning
contaminants
from internal portions of equipment. The method of cleaning internal portions
of
equipment comprises the steps of:
(a) generating a foam comprising a compound capable of reacting with the
contaminant; and
(b) passing the foam through the internal portions of the equipment
wherein the foam is generated external to the equipment.
Still further, the invention is directed to equipment having within its
internal
portions, a foam comprising a compound capable of reacting with a contaminant
wherein the foam is generated external to the equipment.
DETAILED DESCRIPTION OF THE INVENTION
There generally is no limitation with respect to the type of foam being passed
or
circulated through the internal portions of the equipment being cleaned via
this
invention. The only limitation with respect to the foam is that it is able to
carry or
transport the compound capable of reacting (neutralizing/solubilizing) with
the
contaminant targeted for removal within the equipment.
The surfactants which may be used to generate the foam comprising the
compound capable of reacting with a contaminant may be anionic, cationic,
nonionic,
zwitterionic, amphoteric or a mixture thereof. The surfactants are known in
the art and
commercially available from suppliers like Shell Chemical, Witco Chemical
Company,
Dow Chemical, BASF and ICI Surfactants. Such surfactants are only limited to
the
4
CA 02310740 2000-06-06
C6541 (V)
extent that they are capable of generating a foam compatible with the compound
capable of reacting with the contaminant targeted for removal. The anionic
surfactant
which may be used to produce the foam employed in this invention includes at
least
one surfactant selected from the group consisting of a carboxylic acid salt,
like a sodium
and potassium salt of a straight-chain fatty acid, and a sulfonic acid salt,
like a linear
alkylbenzene sulfonate, and an a-olefin sulfonate, and a sulfuric acid ester
salt, like a
sulfated polyoxyethylenated straight-chain alcohol, and phosphoric and
polyphosphoric
acid esters, like a phosphated polyoxyethylenated alcohol or phenol. In such
anionic
surfactants, the carbon chain lengths may vary but often contain from about 5
to about
50 carbon atoms, and preferably, from about 5 to about 25 carbon atoms.
The cationic surfactant which may be used to produce the foam employed in this
invention includes at least one surfactant selected from the group consisting
of a
quarternary ammonium compound with, for example, a halogen as the counterion.
Examples include dodecyl trimethyl ammonium bromide, and polyoxyethylenated
long-
chain amines.
The nonionic surfactant which may be used to produce the foam employed in
this invention includes at least one surfactant selected from the group
consisting of a
polyoxyalkylenated alkylphenol, polyoxyalkylenated straight chain alcohol,
amine oxide,
polyoxyalkylenated polyoxyalkylene glycol, polyoxyalkylenated mercaptan, long-
chain
carboxylic acid ester, alkanolamine condensate and polyoxyalkylenated
silicone. When
the nonionic surfactants are derived from the condensation of ethyleneoxide
with the
product resulting from the reaction of propylene oxide and ethylene diamine
products,
they usually have about 40% to about 80% by weight polyoxyethylene and a
molecular
weight from about 5,000 to about 11,000.
Regarding the zwitterionic surfactants which may be used to produce the foam
employed in this invention, such surfactants include at least one surfactant
selected
5
CA 02310740 2000-06-06
C6541 (V)
from the group consisting of a ~i-N-alkylaminopropionic acid, N-alkyl-~i-
iminodipropionic
acid, imidazoline carboxylate and betaines, like sulfobetaine.
The amphoteric surfactants which may be used in this invention include those
which are classified as derivatives of aliphatic secondary and tertiary amines
in which
the aliphatic radical can be straight or branched, and wherein one of the
aliphatic
substituents contains from about 8 to about 18 carbon atoms and one contains
an
anionic water solubilizing group, like a sulfonate. Illustrative examples of
such
amphoteric surfactants include sodium lauryl sarconsinate, dodecylamine and
isethionate.
A more detailed description of the types of surfactants which may be used in
this
invention may be found in U.S. Patent No. 5,120,532, the disclosure of which
is
incorporated herein by reference.
The only limitation with respect to the amount of surfactant used to make the
foam comprising a compound capable of reacting with the contaminant is that
the
amount selected results in a foam that may be fed through the internal
portions of
equipment. Typically, however, the amount of surfactant used to make the foam
is
from about 0.1% to about 30%, and preferably, from about 0.5% to about 20%,
and
most preferably, from about 2.0% to about 10% by weight, based on total weight
of
the pre-foam composition comprising a compound capable of reacting with a
contaminant, including all ranges subsumed therein. Pre-foam composition, as
used
herein, is the composition that is subjected to air or a gas to generate the
foam
employed in this invention.
In a preferred embodiment, a mixture of anionic and nonionic surfactants is
used. The mixture often comprises an anionic:nonionic surfactant weight ratio
of about
90:10 to about 10:90. Preferably, however, the anionic:nonionic surfactant
weight ratio
6
CA 02310740 2000-06-06
C6541 (V)
is about 40:60 to about 60:40. The preferred surfactants used to prepare the
mixture
of surfactants used in this invention are alcohol ethoxylate and alpha olefin
sulfonate.
The former, for example, is sold under the name of Neodol 91-6 and
commercially
available from Shell Chemical. The later is sold under the name of Witconate
AOS and
commercially available from Witco Chemical Company.
The compound capable of reacting with the contaminant that may be used in this
invention is limited only to the extent that is one which does not destroy the
foam that
the compound is carried in or the equipment being cleaned. Typically, the
compound
capable of reacting with the contaminant is one which reacts with basic
inorganic
contaminants, like calcium carbonate, acidic contaminants, like ascorbic acid
and/or
organic contaminants comprising at least one member selected from the group
consisting of pulp stock, wood pitch, alcohols, anhydrides and the like. The
compounds
capable of reacting with the contaminant which may be used in this invention
include
acids such as acetic acid, citric acid, lactic acid, hydrochloric acid,
sulfuric acid,
phosphoric acid, nitric acid, and preferably, muriatic acid when the
contaminant is, for
example, basic and inorganic. Other compounds capable of reacting with a
contaminant
which may be used in this invention include bases such as potassium hydroxide,
calcium hydroxide, magnesium hydroxide, and preferably, sodium hydroxide when
the
contaminant is, for example, a crystallized acid or organic contaminant. It is
also with
the scope of this invention to use mixtures of the above-identified acids and
bases.
The only limitation with respect to the amount of compound capable of reacting
with a contaminant used in this invention is that the amount selected does not
destroy
the foam that the compound is carried in or the equipment being cleaned.
Typically,
however, the amount of compound used in the foam is from about 20% to about
85%,
and preferably, from about 30% to about 75%, and most preferably, from about
45%
to about 65% by weight, based on total weight of the pre-foam composition
comprising
7
CA 02310740 2000-06-06
C6541 (V)
a compound capable of reacting with a contaminant, including all ranges
subsumed
therein.
Other additives which may be included in the foam comprising a compound
capable of reacting with a contaminant include at least one member selected
from the
group consisting of a foam builder, corrosion inhibitor, stabilizer (e.g.,
mild surfactant),
and colorant, whereby the balance of the foam is typically water.
The foam builders which may be used in the foam comprising a compound
capable of reacting with a contaminant include those that may be classified as
alkylaryl
sulphonic acids such as dodecylbenzine sulfonic acid. When foam builders are
used in
the foam comprising a compound capable of reacting with a contaminant, they
typically
make up from about 0.05% to about 5.0%, and preferably, from about 0.1% to
about
2.0%, and preferably, from about 0.2% to about 1.0% by weight of the pre-foam
composition comprising a compound capable of reacting with a contaminant,
including
all ranges subsumed therein.
The corrosion inhibitors which may be used in this invention include those
that
may be selected from the group consisting of a chromate, phosphate, molybdate,
silicate, amine and mixture thereof. The preferred corrosion inhibitor that
may be used
in this invention is a fatty acid amine sold under the name Rhodine and made
commercially available from Henkel Kommanditgesellschaft auf Aktien. When
corrosion
inhibitors are employed, they typically make up from about 0.1% to about 4.0%,
and
preferably, from about 0.5% to about 3.0%, and most preferably, from about
1.0% to
2.0% by weight of the total weight of the pre-foam composition comprising a
compound capable of reacting with a contaminant, including all ranges subsumed
therein.
8
CA 02310740 2000-06-06
C6541 (V)
The stabilizers which may be used in this invention include those which may be
classified as mild surfactants. Such stabilizers include amphoterics,
betaines, sultaines,
modified guars, alcohol sulfates, cationics, silicones and the like. The
preferred
stabilizers used in this invention include a coconut derived amphoteric sold
under the
name Miranol, betaines or sultaines sold under the name Mirataine and alcohol
sulfates
sold under the name Rhodapon, all of which are commercially available from
Rhodia
Personnel Care. When stabilizers are employed in the foam, they typically make
up
from about 0.1% to about 4.0%, and preferably, from about 0.5% to about 3.0%,
and
most preferably, from about 1.0% to about 2.0% by weight of the total weight
of the
pre-foam composition comprising a compound capable of reacting with a
contaminant,
including all ranges subsumed therein.
There is generally no limitation with respect to the colorants used in the
foam of
this invention. Such colorants may be dye or pigment based and they are
commercially
available. Acid Red #14 is often the most preferred colorant, and the
colorants typically
make up less than about 0.008% by weight of the total weight of the pre-foam
composition comprising a compound capable of reacting with a contaminant.
When preparing the foam used in this invention, the components (e.g.,
surfactant, water, compound capable of reacting with a contaminant) are mixed,
stirred
or agitated using any art recognized technique. The resulting pre-foam
composition
may be made at ambient temperature, atmospheric pressure, or at any pressure
and
temperature variations which may result in a composition that can be
transformed into
a foam. The addition of the components is not limited to any particular order,
with the
proviso that the resulting mixture is one which may be employed to make a
foam.
To prepare the desired foam, air, for example, is driven/pumped into the pre-
foam composition to produce the foam comprising a compound capable of reacting
with
a contaminant of this invention.
9
CA 02310740 2000-06-06
C6541 (V)
The foam comprising the compound capable of reacting with a contaminant may
be a very wet foam, and therefore, froth-like. The foam may also be classified
as a wet
foam, for example, one with spherical bubbles, or a dry foam having polyhedral-
type
bubbles. A more detailed description of the characteristics of the foams which
may be
used in this invention is found in The Enc~rclopedia of Chemical Technology,
Kirk-
Othmer, Vol. li, 4t" Edition (1994), pages 783-804, the disclosure of which is
incorporated herein by reference.
When practicing the invention, the pre-foam composition is transformed into a
foam external to the equipment being cleaned. Thus, air or a gas (e.g.,
nitrogen) is
forced into the pre-foam composition in an external canister or vessel. Once
the foam
is generated, the foam is then fed from the external canister or vessel into
the internal
portions of the equipment being cleaned for a time sufficient to cause a
reaction
between the contaminant in the equipment and the compound capable of reacting
with
the contaminant. This invention which feeds the foam, already generated, into
the
internal portions of equipment ensures that substantially all of the
contaminants within
the equipment are removed uniformly throughout the equipment. The air or gas
that is
forced into the pre-foam composition typically is supplied by a commercially
available
compressor or pneumatic pump that is part of or independent of the equipment
being
cleaned. It is also within the scope of this invention to use a compact foam
generating
apparatus to generate and circulate the foam. Such an apparatus is disclosed
in U.S.
Serial No. , presently Attorney docket No. 99-0390-DIV, commonly
assigned to Diversey Lever, Inc., the disclosure of which is incorporated
herein by
reference.
The amount of air or gas supplied to the pre-foam composition is limited only
to
the extent that the resulting foam can be used to clean the internal portions
of
equipment. Typically, however, the amount of air or gas supplied results in a
foam
CA 02310740 2000-06-06
C6541 (V)
having a bubble diameter from about 0.5 to about 20.0 mm, and preferably, from
about
0.75 to about 15.0 mm, and most preferably, from about 1.0 to about 10.0 mm,
including all ranges subsumed therein.
The only limitation with respect to how fast the foam comprising a compound
capable of reacting with a surfactant is circulated throughout the internal
portions of the
equipment being cleaned is that the velocity selected allows for contaminant
removal.
Typically, however, the foam is circulated throughout the internal portions of
the
equipment being cleaned at a rate from about 0.1 to about 10.0 meters per
minute, and
preferably, from about 0.2 to about 6.0 meters per minute, and most
preferably, from
about 0.3 to about 4.0 meters per minute.
In the most preferred embodiment of this invention, the amount of air or gas
supplied into the pre-foam composition and the velocity of the resulting foam
circulated
throughout the internal portions of the equipment being cleaned are selected
so that
from about 0.3 kg to about 25 kg per minute of contaminant are removed from
the
equipment. Typically, the velocity of the circulating foam is such that an
initial sample
of foam exiting the equipment will have a pH of greater than about 5, and
preferably,
greater than about 6, and most preferably, greater than about 7 when the
compound
capable of reacting with a contaminant is acidic and the contaminant is basic.
When
the compound capable of reacting with the contaminant is basic and the
contaminant is
acidic, the velocity of the circulating foam is such that an initial sample of
foam exiting
the equipment will have a pH of less than about 6, and preferably, less than
about 5,
and most preferably, less than about 4. When the cleaning process is complete,
the
spent foam exiting the equipment that was cleaned typically has a pH of about
1 to
about 4 when the compound capable of reacting with the solvent is basic and
the
contaminant is acidic. On the other hand, when the cleaning process is
complete, the
spent foam exiting the equipment that was cleaned typically has a pH of about
8 to
about 11 when the compound capable of reacting with the contaminant is basic
and the
CA 02310740 2000-06-06
C6541 (V)
contaminant is acidic. It is also noted herein that this invention may be used
in
equipment, like a boiler, cooling tower, food and beverage equipment and pulp
and
paper processing equipment, whereby equipment includes any process lines or
liquor
lines associated therewith.
The following example is provided to illustrate and facilitate an
understanding of
the present invention. The example is not intended to restrict the scope of
this
invention.
EXAMPLE
A mixing vessel was charged with the following components:
_ % b Wei ht
Deionized water 35.795
Alcohol etho later 1.500
AI ha olefin sulfonate 1.500
Coconut am hoteric3 1.500
Corrosion inhibitor4 1.450
Muriatic acid 58.000
Dode I benzene sul honic0.250
acid
Acid red No. 14 0.005
~ Neodol9l-6
2 Witconate AOS
3 Mirataine CB
4 Rhodine 213
The components were stirred at ambient temperature to produce a pre-foam
composition that was subsequently transferred to a shipping container. The
shipping
container was delivered to a mill having a Kraft pulping process green liquor
line
(approximately 1,000 ft. of 25 cm diameter tubing) contaminated with calcium
carbonate (about 1.25 cm to about 2.25 cm) and trace amounts of other
inorganic
contaminants. The pre-foam composition was pumped from the shipping container,
via
a pneumatic pump, into a first inlet of a mixing tee (316 stainless steel
piping, about
2.5 cm in diameter), by way of a chemical resistant hose of about 2.54 cm in
diameter.
12
CA 02310740 2000-06-06
C6541 (V)
A second inlet of the mixing tee was supplied with air from a central air
compressor
(e.g., commercially available by Ingersol Randy, having a nylon air injection
line of
about 1.25 cm, and the air pressure was approximately 60 psig (enough air to
blow the
pre-foam composition to a foam 20 times its liquid volume). The resulting foam
was
generated within the mixing tee and subsequently fed, via a 2.54 cm chemical
resistant
hose, into the green liquor line (by way of the mixing tee outlet) which had
already
been drained and washed with water. The foam was supplied to the green liquor
line at
a rate of about 3 meters per minute, and the foam was circulated throughout
the entire
green liquor line. Upon exiting the green liquor line, the resulting spent
cleaning foam
was tested for pH. An initial sample that exited the line had a pH of about 6.
The
process was completed when, simultaneously, the spent foam had a pH of about 3
and
the green liquor line was substantially free of contaminants based on visual
examination
after a rinse with water. The invention, unexpectedly resulted in a green
liquor line that
was substantially free of contaminants (uniformly throughout) while using 80%
less
fluids than conventional processes. Moreover, the cleaning process was
successful
without installing a pressure relief mechanism into the green liquor line and
without
taking the equipment apart.
13
