Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~Z~3~5
Process and device for loosening and removing solid coatings
on the surfaces of enclosed spaces, e.c~. the flue gas side
of a furnace or boiler
The present invention relates to a process for loosening and
removing solid coatings on the surfaces of enclosed spaces,
e.g. soot and solid coatings formed during the operation of
a furnace ~r boiler on the surfaces of space of the furnace
forming the ~lue gas side, covers and flue gas ducts to the
flue yas side being sealed to form a closed chamber and
steam, saturated with a special cleaning composition accord-
ing to the invention, is supplied to the flue gas side. The
process according to the invention can be carried out in one
or more steps, depending on the composition and thickness of
the coatings.
The invention also comprises a device for carrying out the
process. The invention will be described in more detail
below and illuminated with examples for the case where the
enclosed space, ~he surfaces of which are ~o be freed of
coatings and thus cleaned, is the flue gas side of a
furnace or boiler, but i~ will be obvious that the process
and the device can just as easily be applied to the cleaning
of other enclosed spaces, e.g. the interior walls of tanks
and large vessels.
The background of the invention
Continually rising oil prices make it necessary to try all
possible means to reduce the cost of oil heating of houses,
apartment ~ouses and factories by seeing to it that the
efficiency of the furnaces is as hi~h as possible. Optimum
ener~y use of furnaces means lower fuel cons~nption, lower
maintenance costs and a cleaner environrnent. At the same
time as attempts are made to reduce the direct fuel costs
and increase efficiency of the furnaces, attempts are made
to avoid corrosion on the furnace walls as well. The main
~.
~Z1~3~i
cause of corrosion is the sulphur in -the fuel, primarily
fuel oil. During combus-tion this sulphur forms with the
oxygen in the combustion air sulphur dioxide, which sub-
sequently gives rise to sulphuric acid, which is very
corrosive to the furnace walls. Modern furnaces have a
relatively high efficiency. In a clean oil-burning furnace
about 90 ~ of the heat content of the oil is utilized. When
the oil-is burnedr however, soot is also produced in
addition to heat, and some of this soot is deposited on
the furnace walls, partly in the form of loose soot and
partly as a solid coating. Soot is an extremely good
insulation material, five times better as asbestos. When
the thickness of the soot layer on the walls of the flue
gas space are 2 mm for e~ample, there is a heat transfer
loss in the furnace wall of nearly 20 % and when the
coating thickness is between 3 and 4 ~m, the heat transfer
has reached about 50 %. The problem can also be expressed
as follows: an increase in the flue gas temperature of 50C
from 200C to 250C for example with a carbon dioxide
content of 10 %, reduces the efficiency of the furnace by
about 3 %. This points out the great economic importance of
preventing an unnecessary rise in the -flue gas temperature,
e~g. as a result of reduced heat absorption ~ecause of
solid coatings on the furnace surfaces.
Factors contributing to reduced heating costs in burning
fossil fuels include cleaning and soot removal in furnaces
and removal of solid coatings which appreciably reduce the
heat transfer capacity and thus the efficiency of the
3~ furnace, resulting in turn in higher energy consumption.
The solid coatings on the furnace walls and the convection
portions, consist pri~arily of sulphates, which are very
difficult to remove by conventional mechanical cleaning
methods or b~ traditional sweeping, In certain types of
~5 cast f~lrnaces, the coatings can result in a reduction of
surface area in the flue ~as ducts in the convection portion
-making flue gas evacuation ~ore difficult
3~i
There is no complete knowledge of the contents of combustion
residues in furnaces. Analyses of coatings from oil-burning
units reveal, in addition to combustion residues such as
oil coke and flame soot, also hiyh contents of ash particles,
silicon, asbestos, sodium, calcium, sulphur dioxide ancl
a number of heavy metals such as vanadium, nickel, iron,
copper, cadmiumf lead, zinc, mercury and chromium. Buxning
certain t~pes of fuel o~ls produces relatively high contents
of vanadium, sulphur and iron sulphate in the furnace
coatings. The coatin~s can thus vary widely in chemical
composition. This places great demands on the cleaning agent
The cleaning agent must not be harmful to the furnace nor
to the environment, effectively removing soot and coatings
on furnace walls but at the same time not producing corro-
sion or brittleness of the furnace material.
Several methods are known and generally used for removingsolid coatings in e.g. furnaces n The methods used up co now
are primarily ~ased on the use of a neutralizing agent, i.a.
ammonia, primarily for controlling the pH value of the
cleaning steam to a level which is sufficient to neutralize
the sulphuric acid normally formed when steam comes into
contact with solid coatings. The neutralizing agents used
are inexpensive and easily available and when carefully
used produce rather ~ood cleaning~ Despite this utility,
these neutrali2ing agents have certain disadvantages however
which make their use more difficult and make the cleaning
process less effective.
According to one method, described in Swedish Lay-open Print
7415358~6 (publication number 387 430)~ steam is used to
remove bo~h soot and solid coatings. The method has proved
to be effective and relatively inexpensive.
The method in~olves however subjecting the furnace to a
certain amount of wear at each cleaning. Wear arises because
of corrosion~ since the steam condenses on the furnace walls
~Z~3~S
and reacts with the sulphur compounds in the coatings to
form sulphuric acid. This is highl~ corrosive also in the
drainage system throuyh which the dissolved sludge must be
removed during cleaning. To~neutralize the sllldgel before
it runs out into the drain, caustic soda is usually used,
which is pl~ced on the bottom surface of the furnaee. It
is however difficult to achieve a perfect dosage of so~a
to preven~ environmental damage, due to too high or too low
pH value. Also certain risks are involved for workers
handling the soda. Furthermore it is not possible to
eliminate corrosion on the ~urnace walls with the aia of
the caustic soda. Aftex the steam treatment, the dissolved
coatings are removed by rinsing with water. It is possible
to add a basie agent to the rinse water whieh can neutralize
the sulphuric acid, but the amount of sulphurie acid is
usually so large that too much time must be devoted to
rinsing with a basic a~ent. After water rinsin~, the cleaned
furnace surfaces are treated with an approved basic agent
to neutralize any remaining sulphur in pores, welding joints
and the like~ This method, which is designated System Vapor,
is complicated and expensi~e in addition to having the above
described problems
According to a ~rocess described in Norwegian Patent Speci-
fication ~2654, in cleaning heating surfaces on the flue
gas slde of furnaces, preheaters and the like, one starts
with a mixture consisting of water, preferabl~ in steam
form, and ammonia. Carbon dioxide is added to this mixture
in the form of a gas mixture or a solution of carbonated
ammonium salts and during the period in which this mixture
is allowed to act on the heat s~lraces to be cleaned,
a continuous cooling of the heat surfaces is ef~ected from
the water side by means of water, salt solution, cold air
or otherwise The inventive idea behind the process accord-
ing to the patent specification, is that the added carbondioxide together with the am~onia will achieve an increase
in the inner pressure in the capillaries of the deposits~
~ z~.~3~5
which will lead -to a bursting of the coating. To achieve
this effect, i.e. achieve an additional pressure increase,
the patent specification discloses that the process can be
amplified b~ temporary heatingi This pressure increase
achieved thereby is said to be the cause of the powerful
burstiny effect. The patent speci~ication also discloses
that according to one embodiment of the process, the desired
effect is`~chieved in a more advantageous manner by alter-
natingly cooliny and heating the waterside, the heating
being done by stea~ for example, hot water or the like, and
the cooling being effected in ~arious ways which require
more work, time and expense. According to one embodiment,
it is disclosed that cooling is effected by means o
softened water and salt solution is recommended for cooling
other parts of the flue gas space. The patent specification
also points out that when neutralizing free sulphuric acid
occurring in the deposits, the reaction heat generated has
a disadvantageous effect or a completely inhibiting effect
on the process, especially on the condensation of water
ar~onia vapours which is unavoidable for the process. In
the patented process, the continuous cooling from the water-
side ;s prevented by the heat generation.
~erman ~uslegeschrift 27 0~ 716 describes a process which
is di~ided into several steps. In the first step, ammonia-
water is introduced into the flue gas space in the furnace
by means of steam for a period of 1~2 hours. The ammonia
used is not mixed into the steam before it is introduced
into the flue gas space. Rather~ ammonia vapours are intro-
duced into the upper portion of the flue gas duct to becleaned ~hrough openings designed there~or, and the ammonia
is finally di~ided by means of a spray device for water,
also in the upper portion of the flue gas space. In the
meantime, steam is introduced into the lower portion of
the flue gas duct through steam jets, whereby the steam
produces an additional fine division of the ammonia vapou~.
The Ausle~eschrift discloses that it is advantageous to
~Z~L34~i
arrange the spray device or water as high as possible in
the flue gas space and the injectors as low as possiblP in
the space, so that the water can effect a cleaning process
from top to bottom while the steam flows from bottom to top.
During this step of the total process, there is no satura-
tion o~ steam with neutralizin~ ayent, i.e. c~mmonia. Rather,
it is disclosed that the ammoniawater used suitably has a
25 % contè~t of ammoni~, the rest being water.
After the initial treatment with ammoniawater plus steam,
there is the next step which involYes introduction,
simultaneously wit~ the ammonia ~apour, of water in such
limited amounts that the pH Yalue of the collected dropping
water does not fall below 7.4. It is stated that during
this step it ~s ~ery i~portant that the con-tinued supply of
ammonia vapour be dosed in response to the measured pHvalue.
Then there is the third step in the process, according to
which a small amount of ammonia plus a very large amount
of water is supplied to the flue gas side. It is specified
that initially a very small amount of water is sprayed in,
the proportion of water b~ing continually raised as the
cleaning of the vessel continues.
After the amount ratio ammonia/water has been continually
changed during t~e preceding step to maintain a pH value in
the dropping water of abo~e 7.4, a final water spraying is
done. By way of conclusion~ the process according to the
German Ausle~eschrift is characterized by initially spraying
in ammoniawater which is finally divided by means o
separate steam injected in another part o~ the unit, where-
after a mixture of ammonia and water is introduced, where
the ratio of amount between these two components is
continually regulated to hold the pH above 7.4.
Pinall~, Danish Lay-open Print 122 369 describes an agent
for cleaning the ~lue gas side o~ furnaces. The agent
3~
consists in principle of two components, namely a) ordinary
anionic, amphoteric or non-ionic tensides and b) chemical
compounds which ~o a far reaching degree are subjected to
thermal decomposition with heavy generation of yases,
preferably ammonia and carbon dioxide. According to the
Lay-open print, the following demands are placed on the
means used: 1. it must haYe a high wetting and penetrating
effect, 2,'it must have a good neutralizing effect, 3. ik
must produce a heavy generation of gas at elevated tempera-
ture and finallyr the medi~ must have minimal tendency toform coatings, The inventi~e idea can be said to lie in
point 3, i.e. that the means ~ust produce a heaYy gas
generation at elevated te~peratureD Examples of components
having this characteristic o~ producing heavy gas genera
tion, preferably ammonia and carbondioxide, are ammonium
carbonatel ammonium ~icarbonate, ammonium carbamate or
carba~ide. According to the lay~open print, it is also
possible to use gas generatiIlg compounds which do not split
the ammon;a, i.e. compounds which have been used as blowing
agent in the manufacture of foamed plastic articles. It is
stated that w~ are dealing with compounds which at elevat~d
temperature split off nitrogen, e.g. aæodicarbonamide with
several compounds. According to the lay-open print, it is
also possible to use oxygen generating compounds, e.g.
carbamide peroxide adducts and finally it is also possible
to use a com~ination of substances, which are thermally
decomposed with gas generation.
The description discloses how the cleaning agent in question
can be used: a solution in water or possibly partially a
dispersion of the means being sprayed as such into the flue
gas space o~ the furnacer using for this purpose a spray
device commonly available on the market with su~ficient
capacity, e.g. those available for spraying of gardens
against harmful insects.
All of the known processes and means described above for
34~i
cleaning the flue gas side of furnaces have various dis-
advantages which can be avoided with the present invention.
The present invention relates to a process, according to
which steam, prior to being supplied to the flue gas
side for example of the ~urnace, is saturated with a com-
position which, if the process is carried out in only one
step, or a~ternatively in the first step of a multistep
process, i.a. produces an increase in the pH value of the
]o steam to a level which is sufficient and necessary for
creating a basic environment, in which the components of
the composition during the cleaning process transform all
harmful sulphur compounds in the coatings and environmental-
ly harmful heavy metals into harmless salts which can be
easily remo~ed from the bottom of the furnace. Saturating
the steam with the composition in question practically
completely elim;~natesthe formation of sulphuric acid with
accompanying problems according to the traditional processes.
~ sulphuric acid is still formed upon contact o~ the steam
with the sulphur compounds in the coatings, this acid is
immediately neutralized by alkali in the composition, such
as alkali hydroxide, silicates or phosphates. Normally,
however, as was mentioned, other compounds are formed in
the reaction between the components of the composition and
the sulphur compounds, which will be discussed in more
detail below.
The composition used in the process according to the inven-
tion consists of a mixture, which primarily and in principle
comprises synth~tic tensides, or~anic complexing agents,
alkali which in addition to the aboYe mentioned effects
(i.e. achieving a basic environment and neutralizing any
sulphuric acid formed) also have a direct grease dissolving
and cleaning effect, environmentally safe solvents and
solvent vehicles, corrosion inhibitor, passivating additive,
sur~actants and water. The make up of the composition is
directed in each individual cleaning case to the type of
s
pollutants occurring and the coatings in the spaces to be
cleaned and to the thickness of the coating. In practice,
several steps must often be combined to achieve a satis-
factory clean result. Thus it is not possible -to recommend
a uniform composition for all types of furnace units and
coatings.
When usiny a cleaning process in two steps for a ~urnace
unit for example, the first step is suitably carried out
in a basic en~ironment as mentioned above, while the second
step, for remoYing for example hard to remove burned on
residue on furnace walls, such as oil coke and flame soot
as well as iron sulphate coatings~ is performed in an acid
environment.
Thus the scope of the in~ention encompasses the use of a
number of special cleaning a~ents which best fulfil the
requirements. The in~ention fulfils even present hiyh
environmental standards. This is especially true with
regard to acid components in coatings such as sulphur
compounds and harmful heavy metals such as vanadium, nickel,
iron, copperr cadmium~ lead, zinc~ mercury and other metal
ionsO These are neutralized and converted into harmless
compounds or salts in the cleaning process in one or more
steps, i.e~ before the waste products enter the drainage
system. Our tests have shown that waste products from the
cleaning process contain only half or one fourth of the
amount of environmentally hazardous substances permissible
by the environmental authorities.
The co~positions used in the process accordin~ to the
invention are in the form of premixed additives, either
YiScous liquids or powders, which are mixed with water
be~ore u5e.
For cleanin~ and removing soot ~rom ~urnaces and removin~
coatin~s in lar~e furnace units~ a composition in liquid
3~;
form appears to be advantageous A powder composition has
the advantage that it need not be protected from frost,
which can be important in certain cases.
-
S The process according to the invention in combination withthe special cleaning cvmpositions can be used in closed
tanks for example and all types of combustion systems with
fossil ~-uels ~or achie~i~ a particularly effective cleaning,
soot removal and removal of coatings by means of a non-
damaging treatment, which i,a. eliminates the danger ofcorrosion damage to the metal surfaces. The process is
considera~ly more simple an~ less time-consuming than
methods used up to now and the treatment result is decidedly
better, thus providing economic advantages over traditional
methods. The process according to the invention also
provides an effective corrosion protection of furnace walls
for example. The compositions used according to the inven-
tion are environmentally safe and do not damage hands or
clothings. Nor are they poisonous, thus making handling
~hereof completely safe. For bulk handling however, it is
recommended that protective glasses and rubber gloves be
used to prevent splashing in the eyes or lengthy skin
contact. In the process according to the invention, waste
products from the treatment of furnaces or tanks are
collected on the bottom of the furnace or tank in the form
of a slud~e. No special disposal prescriptions are required
for the bottom sludge, There is no poisonous discharge and
thus no separate drain cleaning or detoxification is re-
quired. At the same time as the metal surface is cleaned
down to the metal in the process according to the invention,
materials which are normally dan~erous in normal cleaning
of furnaces, are converted to harmless salts and enYiron-
mentally safe xesidue. After the cleaning treatment, an
anticorrosi~e surface passivatin~ layer is formed on the
furnace wall, which also has the e~fect that soot will not
fasten as easily to the furnace wall.
ll ~2~13~
Said anticorrosion effect and the formation of a passivating
layer on the furnace wall is suitably achieved by performing
the passivation in a separate step, after the primary clean-
ing process~ By formation of a surface-passivating layer,
the life of the furnace can be appreciably extended. The
passivating layer formed on the ~urnace wall consis-ts of
iron or zinc phosphate and iron oxide and has a weight of
200-lOOO~m~/m . Examples of passi~ating agents will be gi~en
below.
In summary, the process according to the invention has the
following characteristics for furnace cleaning:
1. The furnace is turned of~.
2. The furnace is sealed to form a closed space.
3. Steam, containin~ the cleanin~ composition, is introduced
in a pressureless state to the furnace,
4. The steam splits off all coatings.
5. All coatings fall to the bottom of the furnace where
they are removed.
6. The furnace is thereafter like new (cleaned down to me~
After these steps the burner is adjusted and sealing is
done as needed.
~5
The process is similar when applied to other enclosed spaces
than f~rnaces.
Thus in the process according to the invention, the cleaning
co~position used together with water produces a steam which
is then introduced in a pressureless state into the space
to be cleaned~ e~g. the flue gas space of a furnace.
The steam made up of water and cleaning co~position can be
made accordin~ to two different embodiments within the
scope of the in~ention:
~2~3~;
A) The initially viscous or powder cleaning composition is
dissolved in water of normal pH value and this aqueous
solution together with other steam forming water is vapour-
ized together in a device which also falls within the scope
of the invention and will be described below. The mixed
steam is then lntrod~1ced without pressure into the space
to be cleaned, e.g. the flue gas side of a furnace.
. ~ .
.
B~ The aqueous solution of the cleaning composition is
introduced into the pressureless steam already formed in
the device according to the invention or provided from
another source at the site tin that case being first de-
pressurized1. The ~apourization temperature of the composi-
tion lies sufficiently below the temperature of the steam
so that vapourization of the composition takes place
immediately upon introduction of the steam. The introduction
of the aq~eous solution of the composition into the steam
presents no problen~ since the steam is in a "pressureless
state", i.e. îs at approx~mately ambient pressure. Introduc-
tion can be done by means of a pump for example.
The invention will be illuminated in the following by meansof an example with reference to the accompanying drawing,
which shows a furnace and a de~ice according to the inven-
tion for carrying out the process according to variant A).
The furnace l is provided with a burner 2 which generatesflue gas. These rise upwards in the furnace past a hotwater
heater 3 and leave the ~urnace through a flue duct 4. Unter
normal operation of the urnace, soot and solid coatings 5
are formed~ which lower the efficiency of the hotwater
heater 3. Also, the coatin~s increase the flue gas tempera-
ture signi~icantly, which means both poor use of the fuel
supply and increased wear on the flue gas ducts and chimney.
When the furnace 1 is to be cleaned of the coatings 5, the
burner 2 is t~rned of~ the flue ~s damper i~ closed and
13 ~ 3~S
other openings or covers are closed and sealed. A steam
unit 6 is connected via a steam line 7 to the flue gas
side of the furnace.
According to the idea o~ the invention, the furnace de-
scribed above can instead be another closed space which is
to be cleaned of coatings on the walls.
The steam uni.t 6 is provided with a chamber 8, in which,
accordiny to the embodi.ment shown, an electrode 9 is
arr~nged. This part can be made d~f~erently from that shown
in the drawi.ng. The heating unit can be made as immersion
electrode, using process variant Bl. The composition is thus
introduced in thi.s case in aqueous solution into the steam
via an introduction unit (not shown~ in the steam line 7
after the vapourization chamber 8, by means of which line,
the chamber is connected to the closed space, e.g. the
furnace.
An inlet line 10 for water is connected to the lower end of
the chamber 8. A reduction valve 11 is included in the
inlet line 10, hy means: of which the water flow through
the inlet line 10 can be re~ulated, The reduction valve 11
is also provid~d with a branch 12 for a feeder line 13 for
the cleaning composition 14, which is stored in a container
15. The composition in liquid form, which is produced by
dissolving the initially viscous or powdered composition
in water, is drawn by the flow of water through the reduc-
tion val~e into the cham~er 8 in the steam unit 6. Alter-
nati~ely, a pump (not shown~. in the feeder line 13 can pressthe co~position into the branch 12, when a larye amount of
composition is to be mixed into th.e steam.
The flow of liquid composition 14 into the inlet line 10
can be regulated by a ~alve 16. The flow of the mixture of
composition 14 and water into the chamber 8 can be regulated
by means (not shownl i~n the steam unit 6 for sensing the
, . ,
~%1~L3~S
liquid level in the chamber together with a throttle valve
17. Such a liquid level sensor de~ice should suitably be
included in the device even when using immersion electrodes
for heating in variant Bl.
The reduction valve 11 is provided with a nonreturn valve
(not shown), which pre~ents water from penetrating into the
feeder lih~ 13 for the composition, when the flow to the
chamber 8 is cut off by the val~e 17.
The device can be adapted to closed spaces, e.g. furnaces
of various dimensions by sett~ng the reduction valve 11 for
small flows of water and composition 14 when a small space
is to be cleaned, and for greater flows when a large space,
e.g. an industrial f~lrnace is to be cleaned. When said
setting has been ~ade, the steam formation in the unit 6
has automatically the correct admixture of cleaning
composition.
The steam saturated with the composition according to the
invention u~ually has, in a one step process, a pH value of
between 8 and 14. The steam is condensed in a known manner
on the ~etal walls o~ the flue gas side of a furnace for
example. Surfactants in the composition facilitate penetra-
tion of the composition into layers of soot for example andinto the solid coatings; and tensides and complexing agents
in the composition break down the coatings~ Corrosion
inhibitors in the cleaning composition prevent corrosion
when the metal surfaces a~ter the steam treatment are rinsed
clean in a known manner with plain water.
The process described according to the invention eliminates
the problem of neutralizin~ the coatings removed from a
furnace, for example ~y caustic soda, as is done according
to the prior art. Thus the handlin~ o~ caustic soda is
eliminated and thereby the risk of corrosion damage to the
furnace and drainage system.
34S
The cleaning composition used in the process according to
the invention does not give rise to lime deposits in the
steam unit ~ and the risk of toxic discharge into the
sewage system is eliminated~, It has already been mentioned
S that the process substantially reduces the treatment time
for cleaning over known art. In trials for cleaniny a
furnace of size 1000 Mcal, the time saved o~er ordin~ry
steam cleaning was about 12 hours.
By ~irtue of the ~act that the time consumed per cleaning
operation is thus reduced and the corrosion d~mage is
eliminated, furnaces can be cleaned, for maintaining a high
efficiency, more often than pre~iously at the same cost
as previo~sly.
The adaption of the process to the type of coating to be
removed
As mentioned above, the process according to the invention
is adapted to the nature o~ the coatings to be removed, by
suitable selection of the cleaning composition. In principle,
the process can be divided into for example the following
reaction types;
1. Desulphurization of furnaces for example by the zinc-
carbonate method, the composition being based on basic
zinc carbonate ~ZnCO3), which reacts with damaging
sulphur compounds in alkaline environment by forming
insoluble zinc sulphide (ZnSl.
2. The sulphurization according to the iron(II~hydroxy
method, the composition being based on iron(II)hydroxide
(Fe(OH)2), which reacts with damaging sulphur compounds
in alkaline environment while forming insoluble iron
sulphide (FeS2l.
3. Desulphurization according to the iron(III~oxide method,
the composition being based on colloidal magnetic iron
(III)oxide (Fe3O4~, which transforms damaging sulphur
compounds in alkaline environment into insoluble iron
,:i
~L2~134S
sulphide (FeS2).
4. Desulphurization according to the copper carbonate
method, the composition being based on copper carbonate
(CuCO31, which reacts with damaging sulphur compounds
while forming insoluble coppex sulphide (CuS~.
5. Desulphurization according to the hydrogen peroxide
method, the composition being based on stabilized
hydrogen peroxide (~2~ sodium percarbonate (Na2CO3 -
1.5 H2O2~ or percarbamide ((NH2)2CO H202) and the
capac~ty o~ these compounds to completely oxidize
sulphur compounds into c~mpletely harmless salts.
The following are examples of tensides which can be in-
cluded in the cleanin~ composition;
Hydroxy alkyl-ethyl alkyl amino ethyl glycine, which is an
amphoteric tenside, which is effecti~e in both strongly
alkaline and acidic cleaning agents. It is biodegradable
and non toxic.
Lauryl di~ethyl carboxymethyl ammonium betaine, which is
an amphoteric tenside, which is effective and stable in
both alkaline and acidic environment. It is biodegradable
and non-toxic.
Alkylphenylpolyglycol ether with 10 ethylene oxide groups
in the molecule which is a non-ionic tenside with
especially good cleaning and emulsifying properties. It is
partially biodegradable and non-to~ic.
It is also possible to use combinations of the above
mentioned ~ensides, which have good ~xease, dirt and soot-
3a solving properties and ~re characterized by good penetra-
tion capacity into the pores, cracks and cavities of the
coatings. For example combustion residue in coatings in
a furnace are loosened ~ore rapidly from the metal walls.
An example of ~ co~ined corros~on inhibitor and emulsifier
in the cleaning cwnposition is l--hy~roxyethyl-2-alkyl-
imidazoline, which has ~ood adhesion to all types of metal
~2~L~3~
surfaces.
An example of a complexing a~ent in the composition for
heavy metals in the combustion residue and coatings, such
as copper, cadmium, silver, mercury, lead, nickel and
several other metal ions, is ~-mercaptobenzo-1,3,5-triazine.
Other heavy ~etals in the combustion residues and coatings,
such as calci~m, magnesiu~, iron, copper and several other
metal ions~ form soluble complex salts with ethylene
diamino-tetra acetic acid (EDTA), nitrilo-triacetate (NTA),
diethylene triamino penta acetic acid (DTPE~ or hydroxy-
ethyl-ethylene diamino-triacetic acid ~HEEDTE).
An example of a solvent vehicle in aqueous solutions o~ the
composition is sodium cumol sulfonate, which has good
dispersion properties.
An example of an environmentally safe solvent for grease
and ~uel oils is 1,2-propylene glycol and iso-propanol.
Incineration o~ waste products ~rom the cleaning process
As has already been mentioned, waste products from the
cleaning and treatment o~ ~urnaces for example fall to the
~ottom of the furnace in the form of a slurry which is
removed therefrom. To facilitate the transport of these
waste products, it is possible if desired to dewater and
thicken the slurry ~y adding environmentally safe high-
molecular flocculents based on polyacryl amide. No specialinstructions for handlin~ the waste slurry are required
and as was mentioned abo~e~ there is no toxic discharge,
and therefore no separate discharge purification or
detoxification is required.
The process according to the inYention can be carried out,
as has been ~entioned abo~e, in one or two steps, depending
, . . .
18
3~;
on the composition and thickness of the coatings. Below are
some examples of the make up of the cleaning composition:
1. Cleaning of furnaces ~or~example by using a one step
process
~ Neutralization of steam condensate and removal of soot,
heavy ~eta~s and lighter coatings from furnace walls is
carried out in an alkaline enYironment in a one step process
by using for example the above mentioned zinc carbonate
method, iron(Irlhydroxide method, iron(III~oxide method,
copper carbonate method or the hydrogen peroxide method.
The followin~ cleaning agents, for example, can be used
with advanta~e:
A. Stron~ly alkaline specially composed cleaning agent in
liquid form, designed for neutralization of the drop water
and for removing soot and li~ht coatings in furnaces, by
means of which the appearance of corrosion damage on furnace
walls is eliminated by e~ective desulphurization. Damaging
sulphur compounds are transformed in alkaline environment
by complete oxidation into entirely harmless salts which
end up at the bottom of the furnace where they are removed.
The make up of the composition:
5-10 % by wei~ht hydroxy alkyl-ethyl-alkyl-amino-ethyl~
glycine (about 28 % active su~stance)
3-5 % by weight lauryl di~ethyl carboxymethyl ammonium-
betaine (dimethyl lauryl aminobetaine, about 39 % activesubstance~
2-4 % by weight alkyl phenyl polyglycol ether with 10
ethylene oxide groups in the molecule, about 100 % active
substancel
1~2 % by weight l-hydroxy ethyl~2-alkyl-imidazoline
2-3 % by weight 1-mercapto-benæo-1,3,5-triazine
5-10 % by wei~ht potassilDm hydroxide solution (about 40 %~
19
~Z~3~
5-8 % by weiyht tetra-potassium pyrophosphate
3-5 % by weight zinc carbonate, basic
2-3 % by weight iso-propanol
3-5 % by weight 1,2-propylene ylycol
1-2 ~ by weight ethylene diamine tetra-acetic acid (EDTA)
The rest water ~p to 100 % by weight.
B. Stro~ alkaline cleaning agent in powder form.
A spec.~ally composed cle~ning agent in powder form designed
for neutral;zation of the drop water and for removing soot
and light coatings in furnaces. It provides a non-corrosive
treatment of ~urnaces by e~fecti~e desulphurization of
furnace walls. D~maging sulphur compounds are transformed
in alkali~ne environment into comple~ely harmless salts
which end up in the ~ottom of the furnacel where they are
removed .
The mak.e ~p of the co~position:
10-12 ~ ~y weight triammoni~ dodecylbenzene sulfonate
(about ~2 % acti~e substancel
15-20 % ~y weight sodium cumol sulfonate powder (aboutlO0 %
acti~e suhstancel
10-15 % by wei~ht trisodiu~ phosphate (tertially sodium
phosphate~
8-10 % by weight sodium percarbonate (Na2CO3 1.5 H2O)
2-8 ~ by weight sodi~m hydro~ide in powder form, water-free
35-40 % ~y weight sodium disilicate powder ("sodiumsilicate
powder"
1~2 % by wei~ht ethylene diamine tetra-acetic acid (EDTA~
The rest water up to 100 % by wei~ht.
C. Ne~tral cleaning a~ent in powder form.
This composition is used when;the nature of the coatings
do not require an especially stron~ alkaline cleaning agent
in liguid or powder for~.
The ~ake up of the co~position;
.
~ L3~S
10-12 ~ by weight triammonium dodecylbenzene sulfonate
(about 92 % acti~e substance~
35-50 % by weight sodi~m tripolyphosphate in the form of
water-free powder
7-10 % by weight sodium ~l~conate
20-25 % by weight tetrapotassium pyrophosphate
8~10 % ~y wei~ht percarbamide (NH2~2C0 F~202
The rest water up to 100 % by weight.
2. Cleanin~ by use~of a *wo step process
Cleaning and remo~al of strongly adhering combustion residue
for example on furnace wall.s, such as oil coke and flame
soot as well as iron-sulphate coatings of a thickness of
10 ~m on furnace walls or in other enclosed spaces is suit-
ably done in two steps, the first of which is carried out
in an alkaline environment usin~ the above mentioned means
~or example, the second supplementary step for remoYing
the strongly adhering coatin~s being carried out in an acid
environment. The cleaning steps are then suitably followed
by a passivation step for the ~etal surface.
The ~ollowing cleaning agents, for example, can be used with
advantage:
D. Acidic cleanin~ a~ent in liquid form.
Composite cleaning agent in liquid form for removing iron
sulphate, rust, soot and other coatings in furnaces for
example.
The make up of the composition;
12 % by wei:ght mono~ethyl phosphoric acid ester (short-
chain phosphoric acid ester with about 64 % P205~
12 % by weight dimethyl phosporic acid ester (short-chain
phosphoric acid ester with about 64 % P205)
20 % by wei~ht ortho-phosphoric aci.d, about 85 %
15 % by weight alkylarylsulphonate
21 ~113~
8 ~ by weight alkyl phenyl polyglycolether with 10 ethylene-
oxide groups in the molecule
3 % by weight coconut fatty acid amide polyglycolether
with 4.5 ethylene oxide groups in the molecule
2 % by weight ethylene diaminotetra-acetic acid (EDTA-BVT),
iron(III~complexing agent
2 % by weight diethylene glycol
The rest w~ter up to 100 % by weight.
Passivation of the metal surfaces after cleaning was
achieved with the following agents for example:
E. Alkaline passivating agents.
10 % by weight hydroxy alkyl-ethyl-alkyl-amino-ethyl-glycine
(about 28 % acti~e substance~
5 % by weight alkylphenyl polyglycolether with 10 ethylene
oxide groups in the molecule (about 100 % active substance)
25 % by weight sodium phosphonate
5 % by weight activator AD
10 ~ by weight potassi~m hydroxide solution, about 40 %
3 % by weight iso-propanol
5 % by weight 1,2-propylene glycol
The rest water up to 100 % by weight.
F. Acidic passivating agents.
12 % by wei~ht monomethyl phosphoric acid ester (short-
chain phosphoric acid ester with about 64 % P205~
12 % by weight dimethyl phosphoric acid ester (short-chain
phosphoric acid ester with about 64 % P20
20 % by weight phosphoric acid
5 % by weight acti~ator SD
15 ~ by weight alkylaryl sulphonate
8 % by weight alkylphenyl polyglycolether with 10 ethylene
oxide groups in the molecule
5 % by weight alpha~olefine sulphonate
2 % by weight diethylene glycol
The rest water up to 100 ~ by weight.
