EP0053085A1 - Method of cleaning surfaces soiled by deposits accrued during conbustion of carbon materials - Google Patents

Abstract

A process for cleaning surfaces of installations fouled by products of combustion of carbon-bearing materials, such as in particular boiler combustion chambers, rotary or static heat exchangers, combustion product ducts and flues, electrostatic filters, etc., which are to be cleaned without having to stop the combustion process, in order to maintain maximum thermal efficiency in order thereby to make a substantial energy saving, in which an aqueous solution of ammonium nitrate and potassium nitrate is injected into the installation, the deposited substances being detached from the installation by means of sound sources.

Description

The present invention relates to a method for cleaning the surfaces of an installation, fouled by deposits, including or not, resulting from the combustion of carbonaceous materials, applicable without having to stop the combustion process.

Those skilled in the art know that any combustion operation using carbonaceous materials, whether in the gaseous, liquid or solid state, is generally accompanied, on the one hand, by the emission of gas. more or less hot, on the other hand, from the formation of non-combustible mineral products and unburned carbon products. These products are more or less entrained in the circuits in which the gases are transported and they can either deposit on their surface or react chemically with the materials constituting said surfaces, due to the high temperature and their composition, melt and adhere to these last. We thus created more or less encrusting deposits.

These deposits foul the surfaces with which they are in contact and this can have unfortunate consequences when these surfaces are, as in the case of heat generators, those of exchangers responsible for transmitting a heat flux to a fluid flowing from the other side of surfaces. Indeed, these deposits reduce the transfer coefficient of the surface and lead to a reduction in the heat output of the installations sometimes requiring their shutdown.

It is therefore necessary to periodically clean these dirty surfaces, in order to remove these deposits, or at least to limit the amount to an acceptable value.

It is common practice to perform this cleaning by insufflation on the surface to be cleaned of a pressurized fluid such as vapor, water or air, which acts both or separately as a cooling agent causing a retraction of the deposits and as an agent. mechanical ensuring their disintegration.

However, this method requires the use of fluid circuits under a pressure of several tens of bars, and applies only to the surfaces which can be reached directly by the jet of fluid, thereby ruling out its application to installations having circuits with baffles.

Furthermore, such a method is generally implemented outside any combustion process, that is to say the plant stopped; if not, use blowing heads designed so that they can be exposed to the action of more or less corrosive hot gases without deteriorating.

Another conventional process, and no doubt of a certain efficiency, consists in washing dirty surfaces, but one then comes up against the problem of deposits which dissolve badly or which give rise to acid solutions leading to corrosion and destruction. of the constituent materials of the installation. The disadvantage also lies in the fact that the installation to be cleaned must inevitably be stopped for a fairly long period of time, which causes significant losses in productivity in the case where it is part of a unit. continuously working.

Those skilled in the art also know that they can solve this cleaning problem by blasting the surfaces of the installation. However, such a solution finds its application only in installations of particular constitution and arranged in a suitable manner. Hence the very limited interest in this type of process.

Chemical cleaning can also be used, for example, soaking the surfaces to be cleaned with an ammonia solution to neutralize the sulfuric anhydride present in the deposits to be eliminated. However, this method has the same disadvantages as those mentioned above.

This is why the plaintiff, anxious to make its contribution to a problem all the more important as energy savings, and, therefore, the search for the maximum efficiency of heat exchangers. are an objective for manufacturers today essential, sought and developed a method of cleaning and maintenance in a clean state of surfaces fouled by deposits resulting from the combustion of carbonaceous materials, such that it can be applied without having to stop in general the process of combustion in the installation, that is to say without disturbing the operation of the production units which are under its dependence. This process also has the following advantages: it makes it possible to clean the most adherent deposits on surfaces of difficult access without resorting to the use of washing solutions which create corrosion phenomena or of devices consuming unacceptable amounts of energy and without any particular modification or adaptation of the installation to be cleaned.

This process is characterized in that at least one body is injected into the installation capable of reacting chemically with the carbonaceous and mineral deposits which foul the surfaces and that the particles resulting from the chemical reactions are displaced by phasing with overhead acoustic waves to cause them to be entrained by the flow of air or combustion gases or their fall towards the ashtrays of the installation.

Thus, the cleaning process is characterized, first of all, by injecting into the installation at least one body capable of reacting chemically with the carbonaceous and mineral deposits resulting from the combustion of carbonaceous materials.

The chemical reaction must most generally lead to the oxidation of the deposits. In the case of carbon deposits, there is combustion, therefore, destruction of said deposits; in the case of mineral deposits, an oxidation reaction takes place leading to an increase in volume, and therefore to the disintegration of the crystal structures of the deposits. However, this destruction of the structures can also be induced by chemical reactions of the decomposition reaction type and / or substitution reactions. The chemical reaction must also be able to take place under high temperature chemistry conditions.

From the point of view of the nature of the injected body, the applicant preferably uses an oxidant and in particular a nitrate, or even a mixture of nitrates such as potassium nitrate and nitrate ammonium, which, when used in aqueous solution, has a concentration of about 200 to 300 g / liter.

In some cases, it is preferable, to prevent corrosion, to bring these solutions to a pH greater than 9 by adding ammonia or any other body capable of stabilizing the pH of the deposits.

In addition, the injected body always contains the corrosion inhibitors necessary to avoid chemical attacks on the materials constituting the system. It is also possible to use bodies capable of inducing neutralization and / or substitution reactions. The choice of the constituents of the injected body and the quantities of the injected body also take account of the atmospheric pollution regulations.

Preferably, the body is used in the divided state in order to obtain the largest possible contact surface with carbon and mineral deposits, and, consequently, an accelerated chemical reduction.

This state of division can be further increased by injecting the body in the form of a solution which is atomized by means of ultrasonic atomizers or by any other means capable of ensuring suitable dispersion and the number and geographical location of which are essentially depending on the structure of the installation to be cleaned. However, they are generally placed so that the cloud of corpuscles they produce does not come into contact with the flame resulting from the combustion of carbonaceous materials. The atomizers can be installed specially for the cleaning operation or permanently on the existing openings of the installation, for example on manholes.

The body can be injected continuously throughout the cleaning period or in a scheduled fashion. Thus, under the action of this injection within the hot zone of the installation, the body pulverized and entrained by the gases resulting from the combustion is rapidly brought into contact with the carbonaceous and mineral deposits on which it reacts by causing them combustion or the desired chemical reaction. These reactions cause their fine fragmentation which will favor their subsequent displacement under the action of acoustic waves.

The system to be cleaned being in normal operation during the injection of the body, the temperatures at which the reactions take place are between 300 and 1000 ° C, and these reactions are therefore very fast, and even call for high temperature chemistry.

The second characteristic of the invention therefore consists in displacing the particles resulting from the chemical reactions in order to cause them to entrain in the circuit of the combustion gases or their fall towards the ashtrays of the installation. This setting in motion of the particles is obtained by their putting in phase with air acoustic waves, generated by sources of sound vibrations. These sources emit vibrations of audible frequencies of 250 Hertz, for example. It is in the range of audible frequencies that sound sources are most effective for the intended purpose, but it is possible to use infra or ultra-sound sources for certain deposits.

From the power point of view, a range between 100 and 200 decibels per source must be implemented.

These sources must be in places judiciously chosen according to the characteristics of the installation, the nature, the geographical situation and the quantity of deposits to be eliminated. They are more or less distant from each other according to their radius of action. Their design must be such that they can withstand temperatures up to 1000 ° C without deteriorating. They are placed on the installation at the time of cleaning or remain permanently.

Thus, under the combined action of the injected body and the acoustic waves, the deposits which foul the surfaces of the installation, are reduced to a more or less pulverulent mass of particles which is either entrained by the gases resulting from the combustion. and possibly stopped by electrostatic precipitators, or redeposited in certain places of the installation, for example in the lower parts of the installation where it does not hinder the heat exchanges and can be recovered at any time or during a stop of the 'installation according to the design of the latter.

The present invention is illustrated by the drawings which accompany the application. These drawings represent different types of installations capable of receiving application of the claimed process.

• Figure 1 relates to a large power boiler.
• Figure 2 relates to a small power boiler.
• Figure 3 relates to a refinery furnace.

Figure 1 shows, schematically, a vertical section of a high power boiler (1) equipped with a burner (2) emitting a flame (3) generating hot gases which circulate in the direction of the arrows (4) , accompanied by carbonaceous and mineral products which are deposited on the surfaces (5) of the four exchangers (6). Four sprayers (7) arranged in different places of the boiler inject the body capable of reacting chemically with the deposits which foul the surfaces while five sound sources (8) have been placed on each of the two lateral faces of the installation, parallel to the axis of the burner.

FIG. 2 represents a vertical section of a small power steel boiler (9) for the production of hot water or steam equipped with a burner (10) emitting a flame (11) from which result the gases which circulate following the direction of the arrows (12), leaving a part of the solid products which accompany them on the exchange surfaces (13). To apply the process, three injectors (14) were placed while a sound source (15) was placed between the two tubular bundles of the installation.

FIG. 3 represents a vertical section of a refinery furnace (16) consuming 70 tonnes of heavy fuel oil per day. This oven is equipped with three burners (17) which emit flames (18) in each of the three radiation cells (19). The combustion gases circulate in the direction of the arrows (20) and allow some of the suspended particles to deposit, which they entrain on the surfaces of the exchangers (21). Three sprayers (22) were placed near each of the burners, and a fourth, at the outlet of the cells radiation, while seven sound sources (23) were placed for three of them on one of the side walls of the installation at the level of the cells and, for the other four, at the level of the exchangers (21).

To better understand the invention, two examples of application of the invention are now described.

Example 1:

A conventional superheated water boiler, with a heating power of 10 therms per hour, heated with coal, in permanent service, was treated during operation according to the method of the invention to clean both the radiation and heat exchange.

The process was as follows: 200 liters of a solution containing 155 g / l of ammonium nitrate and 135 g / l of potassium nitrate were injected, brought by adding ammonia at a pH in the region of 9.3 and this, for a period of 60 minutes in four periods of 15 minutes, with a stop of 30 minutes between each injection.

During the injection period, the draft of the boiler was reduced to the minimum in order to avoid loss of body through the chimney and four sound sources installed on the walls of the boiler were activated for 10 seconds every 15 minutes at a frequency of 250 Hz and an intensity of 140 decibels. These sources were kept in service for 24 hours after the end of the injection to complete the cleaning. The particles which detached from the surfaces were entrained by the flow of combustion gases and stopped by an electrostatic precipitator.

The thermal efficiency of the boiler which had dropped to 85% of normal had become close to 98% after treatment.

Example 2:

A refinery oven of the type shown in FIG. 3 consuming 300 tonnes of heavy fuel per day, in service for more than six months, was treated by the process of the invention to ensure the cleaning of the combustion cells and of the exchangers. For this, 5000 liters of a solution containing was injected in five 30-minute periods, separated by 30-minute rest periods. 115 g / 1 of ammonium nitrate and 135 g / 1 of potassium nitrate brought to a pH of 9.3 by addition of ammonia.

Following each injection period, seven sound sources distributed according to FIG. 3 were activated for 15 seconds. After entrainment of the particles by the fumes or their deposition at the bottom of the installation, the thermal efficiency of the The installation, which had dropped to 80%, has returned to 95% of normal.

This process finds its application in the cleaning of the surfaces of installations such as, in particular, boiler combustion chambers, rotary or static heat exchangers, flues and smoke ducts, electrostatic filters, and on which we want to intervene without having to stop the combustion process and maintain maximum heat output in order to achieve significant energy savings.

Claims (12)

1. A method of cleaning the surfaces of an installation, fouled by deposits resulting from the combustion of carbonaceous materials, characterized in that one injects into the installation, in the form of a dispersion which is entrained by the gases of combustion, a solution of at least one body capable of reacting chemically with the carbonaceous and mineral deposits which foul the said surfaces, and that the particles resulting from the chemical reactions are displaced by phasing with aerial acoustic waves, in order to cause their entrainment by the flow of air or combustion gases or their fall towards the ashtrays of the installation. 2. Method according to claim 1, characterized in that one injects a solution of at least one body capable of giving with the deposits to be eliminated decomposition and / or substitution reactions. 3. Method according to claim 1, characterized in that one injects a solution of at least one body reacting under the chemical conditions of high temperatures. 4. Method according to claim 1, characterized in that a solution of at least one oxidizing body is injected. 5. Method according to claim 4, characterized in that an aqueous solution is injected containing 200 to 300 g / 1 of ammonium nitrate. 6. Method according to claim 4, characterized in that a solution of a mixture of potassium nitrate and ammonium nitrate is injected. 7. Method according to claim 1, characterized in that the aqueous solution is brought to a pH greater than 9 by addition of ammonia or any other body capable of stabilizing the pH of the deposits. 8. Method according to claim 1, characterized in that one injects a solution of at least one body mixed with corrosion inhibitors. 9. Method according to claim 1, characterized in that the solution is injected outside the combustion zones. 10. Method according to claim 1, characterized in that the phasing of the particles is carried out with waves of audible frequencies. He. Method according to claim 1, characterized in that the acoustic waves are emitted by sources of sound vibrations each having a power of between 100 and 200 decibels. 12. The method of claim 11, characterized in that the sources of sound vibrations withstand temperatures up to 1000 ° C.

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