EP0079338B1

EP0079338B1 - Process and device for loosening and removing solid coatings on the surfaces of enclosed spaces, e.g. the flue gas side of a furnace or boiler

Info

Publication number: EP0079338B1
Application number: EP19820901377
Authority: EP
Inventors: Joe Inge Olgarth Johannesson; Bengt Göran LUNDSTRÖM; Sven-Gunnar Svensson; Sven-Erik Agertegh; Sven-Roland Agertegh; Vlastimir Mikulasek
Original assignee: CLIMATIC AB; DALF INTERNATIONAL AB
Current assignee: CLIMATIC AB; DALF INTERNATIONAL AB
Priority date: 1981-05-20
Filing date: 1982-04-19
Publication date: 1985-07-24
Also published as: FI75594B; DE3264872D1; SE437032B; SE8103177L; EP0079338A1; WO1982004065A1; CA1211345A; FI830144A0; DK11583A; FI830144L; FI75594C; DK11583D0; SE8106333L; DK156677B; DK156677C

Abstract

Process and device for loosening and removing soot and solid coatings on surfaces in enclosed spaces such as the flue gas side of a furnace or boiler. In the case of a furnace, covers and flue gas ducts (4) to the flue gas side are sealed to form a closed chamber, which is supplied with unpressurized steam. Characterizing the process is that the steam, before being introduced into the enclosed space, is saturated with a cleaning composition (14), which includes synthetic tensides, alkali, complexing agents, a corrosion inhibitor and environmentally safe solvents and solvent vehicles. The cleaning of the metal surface is done in one or more steps and is followed by a passivating step for the metal surface, whereby the surface is coated with a passivating agent which counteracts continued deposits on the metal surface. The device is characterized in that it comprises a vessel (15) for liquid cleaning composition (14), said vessel being connected via a line (13) to a reduction valve (11), through which water flows to a steam generating chamber (8), which includes means (9) for vapourizing the water in conjunction with said composition. The combined steam of water and composition is conducted via a steam line (7) to the enclosed space to be cleaned, e.g. the flue gas side of a furnace (1).

Description

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 or boiler on the surfaces of the furnace forming the flue gas side, the covers and flue gas ducts to the flue gas side being sealed to form a closed chamber and steam, saturated with a special cleaning composition according 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, the surfaces of which are to be freed of coatings and thus cleaned, is the flue gas side of a furnace or boiler, but it 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 houses and factories by seeing to it that the efficiency of the furnaces is as high as possible. Optimum energy use of furnaces means lower fuel consumption, lower maintenance costs and a cleaner environment. At the same time as attempts are made to reduce the direct ful costs and increase efficiency of the furnaces, attempts are made to avoid corrosion on the furnace walls as well. The main cause of corrosion is the sulphur in the fuel, primarily fuel oil. During combustion this sulphur forms with the oxygen in the combustion air sulphur dioxide, which subsequently gives rise to sulphuric acid, which is very corrosive to the furnance 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 burned, 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 example, there is a heat transfer loss in the furnace wall of nearly 20 % and when the coating thickness is between 3 and 4 mm, the heat transfer has reached about 50 %. The problem can also be expressed as follows: an increase in the flue gas temperature of 50°C from 200°C to 250°C 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 because 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 furnance, resulting in turn in higher energy consumption. The solid coatings on the furnace walls and the convection portions, consist primarily of sulphates, which are very difficult to remove by conventional mechanical cleaning methods or by traditional sweeping. In certain types of cast furnaces, the coatings can result in a reduction of surface area in the flue gas ducts in the convection portion making flue gas evacuation more difficult.
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 high contents of ash particles, silicon, asbestos, sodium, calcium, sulphur dioxide and a number of heavy metals such as vanadium, nickel, iron, copper, cadmium, lead, zinc, mercury and chromium. Burning certain types of fuel oils produces relatively high contents of vanadium, sulphur and iron sulphate in the furnace coatings. The coatings 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 corrosion or brittleness of the furnace material.
Several methods are known and generally used for removing solid coatings in e.g. furnaces. The methods used up to now are primarily based 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 good cleaning. Despite this utility, these neutralizing 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 both soot and solid coatings. The method has proved to be effective and relatively inexpensive.
The method involves 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 and reacts with the sulphur compounds in the coatings to form sulphuric acid. This is highly corrosive also in the drainage system through which the dissolved sludge must be removed during cleaning. To neutralize the sludge, before it runs out into the drain, caustic soda is usually used, which is placed on the bottom surface of the furnace, It is however difficult to achieve a perfect dosage of soda to prevent 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 furnace walls with the aid of the caustic soda. After the steam treatment, the dissolved coatings are removed by rinsing with water. It is possible to add a basic agent to the rinse water which can neutralize the sulphuric acid, but the amount of sulphuric acid is usually so large that too much time must be devoted to rinsing with a basic agent. After water rinsing, 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 expensive in addition to having the above described problems.
According to a process described in Norwegian Patent Specification 82654, in cleaning heating surfaces on the flue gas side of furnaces, preheaters and the like, one starts with a mixture consisting of water, preferably 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 surfaces to be cleaned, a continuous cooling of the heat surfaces is effected from the water side by means of water, salt solution, cold air or otherwise. The inventive idea behind the process according to the patent specification, it is that the added carbon dioxide together with the ammonia will achieve an increase in the inner pressure in the capillaries of the deposits, 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 by temporary heating. This pressure increase achieved thereby is said to be the cause of the powerful bursting effect. The patent specification also discloses that according to one embodiment of the process, the desired effect is achieved in a more advantageous manner by alternatingly cooling and heating the waterside, the heating being done by steam for example, hot water or the like, and the cooling being effected in various ways which require more work, time and expense. According to one embodiment, it is disclosed that cooling is effected by means of 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 ammonia vapours which is unavoidable for the process. In the patented process, the continuous cooling from the waterside is prevented by the heat generation.
German Auslegeschrift 27 02 716 describes a process which is divided 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 introduced into the upper portion of the flue gas duct to be cleaned through openings designed therefor, and the ammonia is finally divided 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 vapours. The Auslegeschrift discloses that it is advantageous to arrange the spray device for water as high as possible in the flue gas space and the injectors as low as possible 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 saturation of steam with neutralizing agent, i.e. ammonia. Rather, it is disclosed that the ammonia-water used suitably has a 25 % content of ammonia, the rest being water.
After the initial treatment with ammonia-water plus steam, there is the next step which involves introduction, simultaneously with the ammonia vapour, of water in such limited amounts that the pH value of the collected dropping water does not fall below 7.4. It is stated that during this step it is very important that the continued supply to ammonia vapour be dosed in response to the measured pH value.
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 being continually raised as the cleaning of the vessel continues.
After the amount ratio ammonia/water has been continually changed during the preceding step to maintain a pH value in the dropping water of above 7.4, a final water spraying is done. By way of conclusion, the process according to the German Auslegeschrift is characterized by initially spraying in ammoniawater which is finally divided by means of separate steam injected in another part of the unit, whereafter 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.
Finally, Danish Lay-open Print 122 969 describes an agent for cleaning the flue gas side of furnaces. The agent consists in principle of two components, namely a) ordinary anionic, amphoteric or non-ionic tensides and b) chemical compounds which to a far reaching degree are subjected to thermal decomposition with heavy generation of gases, preferably ammonia and carbon dioxide. According to the Lay-open print, the following demands are placed on the means used: 1. it must have a high wetting and penetrating effect, 2. it must have a good neutralizing effect, 3. it must produce a heavy generation of gas at elevated temperature and finally, the medium must have minimal tendency to form coatings. The inventive idea can be said to lie in point 3, i.e. that the means must produce a heavy gas generation at elevated temperature. Examples of components having this characteristic of producing heavy gas generation, preferably ammonia and carbondioxide, are ammonium carbonate, ammonium bicarbonate, ammonium carbamate or carbamide. According to the lay-open print, it is also possible to use gas generating compounds which do not split the ammonia, i.e. compounds which have been used as blowing agent in the manufacture of foamed plastic articles. It is stated that we are dealing with compounds which are elevated temperature split off nitrogen, e.g. azodicarbonamide 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 combination 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 of the furnace, using for this purpose a spray device commonly available on the market with sufficient capacity, e.g. those available for spraying of gardens against harmful insects.
All of the known processes and means described above for cleaning the flue gas side of furnaces have various disadvantages 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 furnace, is saturated with a composition which, if the process is carried out in only one step, or alternatively in the first step of a multistep process, i.a. produces an increase in the pH value of the 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 environmentally harmful heavy metals into harmless salts which can be easily removed from the bottom of the furnace. Saturating the steam with the composition in question practically completely eliminates the formation of sulphuric acid with accompanying problems according to the traditional processes. If sulphuric acid is still formed upon contact of 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 invention consists of a mixture, which primarily and in principle comprises synthetic tensides, organic complexing agents, alkali which in addition to the above 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, and water. The make up of the composition is directed in each individual cleaning case to the type of 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 satisfactory clean result. Thus it is not possible to recommend a uniform composition for all types of furnance units and coatings.
When using a cleaning process in two steps for a furnance unit for example, the first step is suitably carried out in a basic environment as mentioned above, while the second step, for removing 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 invention encompasses the use of a number of special cleaning agents which best fulfil the requirements. The invention fulfils even present high 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, copper, cadium, lead, zinc, mercury and other metal ions. 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 compositions used in the process according to the invention are in the form of premixed additives, either viscous liquids or powders, which are mixed with water before use.
For cleaning and removing soot from furnaces and removing coatings in large furnace units, a composition in liquid 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.
The process according to the invention in combination with the special cleaning compositions can be used in closed tanks for example and all types of combustion systems with fossil fuels for achieving a particularly effective cleaning, soot removal and removal of coatings by means of a non-damaging treatment, which i.a. eliminates the danger of corrosion damage to the metal surfaces. The process is considerably more simple and less time-consuming than methods used up to now and the treatment result is decidely 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 invention are environmentally safe and do not damage hands or clothings. Nor are they poisonous, thus making handling thereof 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 sludge. No special disposal prescriptions are required for the bottom sludge. There is no poisonous discharge and thus no separate drain cleaning or detoxification is required. 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 dangerous in normal cleaning of furnaces, are converted to harmless salts and environmentally safe residue. After the cleaning treatment, an anticorrosive surface passivating layer is formed on the furnace wall, which also has the effect that soot will not fasten as easily to the furnace wall.
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 cleaning process. By formation of a surface-passivating layer, the life of the furnace can be appreciably extended. The passivating layer formed on the furnace wall consists of iron or zinc phosphate and iron oxide and has a weight of 200-1000 mg/m². Examples of passivating agents will be given below. In summary, the process according to the invention has the following characteristics for furnace cleaning:

1. The furnace is turned off.
2 The furnace is sealed to form a closed space.
3. Steam, containing the cleaning composition, is introduced in an unpressurized 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 metal).

After these steps the burner is adjusted and sealing is done as needed.
The process is similar when applied to other enclosed spaces than furnaces.
Thus in the process according to the invention, the cleaning composition used together with water produces a steam which is then introduced in an unpressurized state into the space to be cleaned, e.g. the flue gas space of a furnace.
The steam made up of water and cleaning composition can be made according to two different embodiments within the scope of the invention:

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 vapourized together in a device which also falls within the scope of the invention and will be described below. The mixed steam is then introduced 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 (in that case being first depressurized). The vaporization temperature of the composition 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 aqueous solution of the composition into the steam presents no problem since the steam is in a "pressureless state", i.e. is at approximately ambient pressure. Introduction can be done by means of a pump for example.

The invention will be illuminated in the following by means of an example with reference to the accompanying drawing, which shows a furnace and a device according to the invention for carrying out the process according to variant A).
The furnace 1 is provided with a burner 2 which generates flue gas. These rise upwards in the furnace past a hotwater heater 3 and leave the furnace through a flue duct 4. Under normal operation of the furnace, soot and solid coatings 5 are formed, which lower the efficiency of the hotwater heater 3. Also, the coatings increase the flue gas temperature significantly, 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 turned off, the flue gas damper is closed and 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 of the invention, the furnace described above can instead be another closed space which is to be cleaned of coatings on the walls.
The steam unit 6 is provided with a chamber 8, in which, according to the embodiment shown, an electrode 9 is arranged. This part can be made differently from that shown in the drawing. The heating unit can be made as immersion electrode, using process variant B). The composition is thus introduced in this 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, by means of which the water flow through the inlet line 10 can be regulated. The reduction valve 11 is also provided 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 reduction valve into the chamber 8 in the steam unit 6. Alternatively, a pump (not shown) in the feeder line 13 can press the composition into the branch 12, when a large amount of composition is to be mixed into the steam.
The flow of liquid composition 14 into the inlet line 10 can be regulated by a valve 16. The flow of the mixture of composition 14 and water into the chamber 8 can be regulated by means (not shown) in the steam unit 6 for sensing the liquid level in the chamber together with a throttle valve 17. Such a liquid level sensor device should suitably be included in the device even when using immersion electrodes for heating in variant B).
The reduction valve 11 is provided with a nonreturn valve (not shown), which prevents water from penetrating into the feeder line 13 for the composition, when the flow to the chamber 8 is cut off by the valve 17.
The device can be adapted to close spaces, e.g. furnaces of various dimensions by setting the reduction valve 11 for small flows of water and composition 14 when a small space is to be cleaned, and for greaterflows when a large space, e.g. an industrial furnace is to be cleaned. When said setting has been made, 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 usually has, in a one step process, a pH value of between 8 and 14. The steam is condensed in a known manner on the metal walls of the flue gas side of a furnace for example. Surfactants in the composition facilitate penetration of the composition into layers of soot for example and into 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 after the steam treatment are rinsed clean in a known manner with plain water.
The process described according to the invention eliminates the problem of neutralizing the coatings removed from a furnace, for example by caustic soda, as is done according to the prior art. Thus the handling of caustic soda is eliminated and therbey the risk of corrosion damage to the furnace and drainage system.
The cleaning composition used in the process according to the invention does not give rise to lime deposits in the steam unit 6 and the risk of toxic discharge into the sewage system is eliminated. It has already been mentioned that the process substantially reduces the treatment time for cleaning over known art. In trials for cleaning a furnace of size 1000 Mcal, the time saved over ordinary steam cleaning was about 12 hours.
By virtue of the fact that the time consumed per cleaning operation is thus reduced and the corrosion damage is eliminated, furnaces can be cleaned, for maintaining a high efficiency, more often than previously at the same cost as previously.

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 of 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 (ZnC0₃), which reacts with damage sulphur compounds in alkaline environment by forming insoluble zinc sulphide (ZnS).
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 (FeS₂).
3. Desulphurization according to the iron (III)oxide method, the composition being based on colloidal magnetic iron (III)oxide (Fe₃0₄), which transforms damaging sulphur compounds in alkaline environment into insoluble iron sulphide (FeS₂).
4. Desulphurization according to the copper carbonate method, the composition being based on copper carbonate (CuC0₃), which reacts with damaging sulphur compounds while forming insoluble copper sulphide (CuS).
5. Desulphurization according to the hydrogen peroxide method, the composition being based on stabilized hydrogen peroxide (H₂0₂), sodium percarbonate (Na2C03. 1.5 H₂0₂) or percarbamide ((NH₂)₂CO H₂O₂) and the capacity of these compounds to completely oxidize sulphur compounds into completely harmless salts.

The following are examples of tensides which can be included in the cleaning composition: Hydroxy alkyl ethyl alkyl amino ethyl glycine, which is an amphoteric tenside, which is effective in both strongly alkaline and acidic cleaning agents. It is biodegradable and non-toxic.
Lauryl dimethyl 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 either 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-toxic.
It is also possible to use combinations of the above mentioned tensides, which have good grease, dirt and soot-solving properties and are characterized by good penetration capacity into the pores, cracks and cavities of the coatings. For example combustion residue in coatings in a furnace are loosened more rapidly from the metal walls.
An example of a corrosion inhibitor with emulsifying properties in the cleaning composition is 1-hydroxyethyl-2-alkyl-imidazoline, which has good adhesion to all types of metal surfaces.
An example of a complexing agent 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 2-mercaptobenzo-1,3,5-triazine.
Other heavy metals in the combustion residues and coatings, such as calcium, magnesium, 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 hydroxyethyl-ethylene diamino-triacetic acid (HEEDTE).
An example of a solvent vehicle in aqueous solutions of the composition is sodium cumol sulfonate, which has good dispersion properties.
An example of an environmentally safe solvent for grease and fuel oils is 1,2-propylene glycol and iso-propanol.

Incineration of waste products from the cleaning process

As has already been mentioned, waste products from the cleaning and treatment of furnaces for example fall to the bottom 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 by adding environmentally safe high-molecular flocculents based on polyacryl amide. No special instructions for handling the waste slurry are required and as was mentioned above, there is no toxic discharge, and therefore no separate discharge purification or detoxification is required.
The process according to the invention can be carried out, as has been mentioned above, in one or two steps, depending on the composition and thickness of the coatings. Below are some examples of the make up of the cleaning composition:

1. Cleaning of furnaces for example by using a one step process

Neutralization of steam condensate and removal of soot, heavy metals and lighter coatings from furnace walls is carried out in an alkaline environment in a one step process by using an example the above mentioned zinc carbonate method, iron (II)hydroxide method, iron (III)oxide method, copper carbonate method or the hydrogen peroxide method.
The following cleaning agents, for example, can be used with advantage:

A. Strongly alkaline specially composed 'cleaning agent in liquid form, designed for neutralization of the drop water and for removing soot and light coatings in furnaces, by means of which the appearance of corrosion damage on furnace walls is eliminated by effective 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 weight hydroxy alkyl-ethyl-alkylamino-ethyl-glycine (about 28 % active substance)
3-5 % by weight lauryl dimethyl carboxymethyl ammonium-betaine (dimethyl lauryl aminobetaine, about 39 % active substance)
2-4 % by weight alkyl phenyl polyglycol either with 10 ethylene oxide groups in the molecule, about 100 % active substance)
1-2 % by weight 1-hydroxy ethyl-2-alkyl- imidazoline
2-3 % by weight 1-mercapto-benzo-1,3,5-triazine
5-10 % by weight potassium hyroxide solution (about 40 %)
5-8 % by weight tetra-potassium pyrophosphate
3-5 % by weight zinc carbonate, basic
2-3 % by weight iso-propanol
3-5 % by weight 1,2-propylene glycol
1-2 % by weight ethylene diamine tetra-acetic acid (EDTA)

The rest water up to 100 % by weight.

B. Strongly alkaline cleaning agent in powder form.

A specially composed cleaning agent in powder form designed for neutralization of the drop water and for removing soot and light coatings in furnaces. It provides a non-corrosive treatment of furnaces by effective desulphurization of furnace walls. Damaging sulphur compounds are transformed in alkaline environment into completely harmless salts which end up in the bottom of the furnace, where they are removed.
The make up of the composition:

10-12 % by weight triammonium dodecylbenzene sulfonate (about 92 % active substance)
15-20 % by weight sodium cumol sulfonate powder (about 100 % active substance)
10-15 % by weight trisodium phosphate (tertially sodium phosphate)
8-10 % by weight sodium percarbonate (Na2CO3' 1.5 H₂0)
2-8 % by weight sodium hydroxide in powder form, water-free
35-40 % by weight sodium disilicate powder ("sodium silicate powder")
1-2 % by weight ethylene diamine tetra-acetic acid (EDTA)

The rest water up to 100 % by weight.

C. Neutral cleaning agent in powder form.

This composition is used when the nature of the coatings do not require an especially strong alkaline cleaning agent in liquid or powder form.
The make up of the composition:

10-12 % by weight triammonium dodecylbenzene sulfonate (about 92 % active substance)
35-50 % by weight sodium tripolyphosphate in the form of water-free powder.
7-10 % by weight sodium gluconate
20-25 % by weight tetrapotassium pyrophosphate
8-10 % by weight percarbamide (NH₂)₂CO · H₂0₂

The rest water up to 100 % by weight

2. Cleaning by use of a two step process

Cleaning and removal of strongly adhering combustion residue for example on furnace walls, such as oil coke and flame soot as well as iron-sulphate coatings of a thickness of 10 mm on furnace walls or in other enclosed spaces is suitably done in two steps, the first of which is carried out in an alkaline environment using the above mentioned means for example, the second supplementary step for removing the strongly adhering coatings being carried out in an acid environment. The cleaning steps are then suitably followed by a passivation step for the metal surface.
The following cleaning agents, for example, can be used with advantage:

D. Acidic cleaning agent in liquid form.

Composition 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 weight 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 % P₂ ⁰ _S)
20 % by weight ortho-phosphoric acid, about 85 %
15 % by weight alkylarylsulphonate
8 % by weight alkyl phenyl polyglycolether with 10 ethyleneneoxide 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 water 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-alkylamino-ethyl-glycine (about 28 % active 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 potassium 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 weight 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 % P₂0₅1
20 % by weight phosphoric acid
5 % by weight activator 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.

Claims

1. Process for loosening and removing soot and solid coatings on surfaces in enclosed spaces such as the flue gas side in a furnace or boiler, the covers and flue gas ducts to the flue gas side having been sealed to form a closed chamber, by introduction of steam into the enclosed space, characterized in that the steam, before being introduced into the enclosed space, is saturated with an aqueous composition, which includes synthetic tensides, alkali such as alkali hydroxide, silicates and phosphates, organic complexing agents, environmentally safe solvent and solvent vehicle, a corrosion inhibitor to prevent corrosion on the metal surfaces when they are rinsed with plain water in a known manner after the steam treatment, followed by the steam, saturated with the vaporized cleaning composition, being introduced in unpressurized state, i.e. at approximately ambient pressure, into the space to be cleaned, said process being carried out in one or more steps, whereby in the case of only one step, this is carried out under alkaline conditions and in the case of more than one step the first step is likewise carried out under alkaline conditions, the last cleaning step being followed by a surface passivating step for the cleaned surfaces involving supplying a passivating agent thereto which counteracts the continued coating of the metal surfaces by the formation of a passivating layer consisting of iron or zinc phosphate and iron oxide and having a weight of 200-1000 mg/m².

2. Process according to claim 1, characterized in that the steam saturated with the composition is achieved by supplying an aqueous solution of the composition (14) to the water for vapourization and is vapourized together therewith in a steam generating chamber (8) within a steam unit (6), whereafter the steam of water and composition is introduced via a common steam conduit (7) in an unpressurized state into the enclosed space.

3. Process according to claim 2, characterized in that the enclosed space is the flue gas side of a furnace (1).

4. Process according to claim 1, characterized in that the steam saturated with the composition is achieved by introducing an aqueous solution of the composition in a known manner per se into the steam which is already in an unpressurized state, whereby the aqueous composition is vapourized and the mixed steam is thereafter introduced in an unpressurized state into the enclosed space.

5. Process according to claim 4, characterized in that the enclosed space is the flue gas side of a furnace (1).

6. Process according to one of claims 1-5, characterized in that the cleaning portion of the process is carried out in one step in an alkaline environment, prior to the passivating step.

7. Process according to one of claims 1-5, characterized in that the cleaning portion of the process is carried out in two steps, the first being in an alkaline environment and the other in an acidic environment, prior to the passivating step.

8. Device for carrying out the process according to any one of claims 1-3, characterized in that it comprises a vessel (15) for a liquid composition (14), said vessel being connected via a line (13) to a reduction valve (11), through which water flows via a line (10) to a steam unit (6) comprising a steam generating chamber (8), which contains means (9) for vaporizing the water in conjunction with said composition, the feeder line (13) being provided with a valve (16) for regulating the flow of the composition (14) into a common line (10) forthe supply of the water and composition to the steam generating chamber (8), said steam unit (6) comprising means for sensing the liquid level in the chamber (8) for regulating the flow of the mixture of composition and water to the steam unit (6), said reduction valve (11) being provided with a non-return valve to prevent water from penetrating into the feeder line (13) for the composition when the flow to the steam generating chamber (8) is cut off by a valve (17) disposed in the line (10) between the reduction valve (11) and the steam generating chamber (8).