Chlorine corrosion of pipes in boilers. Corrosion of hot water boilers - the result of using poor-quality water. Corrosion phenomena in boilers are most often manifested on the inner heat-shown surface and relatively less - on the outer
Owners of the patent RU 2503747:
Technicia
The invention relates to heat and can be used to protect against scale heating pipes of steam and water boilers, heat exchangers, boiler installations, evaporators, heating mains, heating systems residential houses and industrial facilities in the current operation.
BACKGROUND
Operation of steam boilers is associated with the simultaneous impact of high temperatures, pressure, mechanical stresses and an aggressive medium, which is boiler water. Boiler and metal surfaces of the boiler are separate phases of a complex system that is formed during their contact. The result of the interaction of these phases is superficial processes arising at the border of their partition. As a result, in the metal surfaces of heating, the phenomena of corrosion and the formation of scale are arising, which leads to a change in the structure and mechanical properties of the metal, and which contributes to the development of various damage. Since the thermal conductivity of the scale is fifty times lower than that of iron of heating pipes, there are a thermal energy loss during heat transfer - with a thickness of 1 mm from 7 to 12%, and at 3 mm - 25%. Strong formation of scale in the system of steam boiler of continuous action often leads to a stop of production for several days a year to remove scale.
The quality of nutritious and, therefore, boiler water is determined by the presence of impurities that can cause different kinds The corrosion of the metal of the inner surfaces of heating, the formation of primary scale on them, as well as the sludge as the source of the formation of secondary scale. In addition, the quality of the boiler water depends on the properties of substances resulting from surface phenomena during the transportation of water, and condensate through pipelines, in water processing processes. Removal of impurities nutrient water It is one of the ways to prevent the formation of scale and corrosion and is carried out by the methods of preliminary (rot) water treatment, which are directed to the maximum removal of impurities in its original water. However, the methods used do not fully eliminate the content of impurities in water, which is associated not only with the difficulties of a technical nature, but also the economic feasibility of applying methods for water treatment. In addition, since water treatment is a complex technical system, it is redundant for boilers of small and medium performance.
Famous methods for removing already formed deposits are mainly used mechanical and chemical cleaning methods. The disadvantage of these methods is that they cannot be made during the operation of boilers. In addition, methods of chemical purification often require the use of expensive chemicals.
Also known ways to prevent the formation of scale and corrosion carried out during the work of the boilers.
US 1877389 patent proposed a method for removing scale and preventing its education in water heating and steam boilers. In this method, the surface of the boiler is a cathode, and the anode is placed inside the pipeline. The method is to pass a permanent or alternating current through the system. The authors note that the mechanism of action of the method is that under the action of electric current on the surface of the boiler, gas bubbles are formed, which lead to the detachment of the existing scale and prevent the formation of a new one. The disadvantage of this method is the need to constantly maintain the flow of electrical current in the system.
In Patent US 5667677, a method is proposed for processing fluid, in particular water, in the pipeline in order to slow down the scale of scale. This method is based on the creation of an electromagnetic field in the pipes, which repels the calcium ions dissolved in water, magnesium walls from the walls of pipes and equipment, not allowing them to crystallize in the form of scale, which allows to operate boilers, boilers, heat exchangers, rigid water cooling systems. The disadvantage of this method is the high cost and complexity of the equipment used.
In the application WO 2004016833, a method for reducing the formation of scale on a metal surface is proposed to exposed to an intersted alkaline aqueous solution, which is capable of forming a scale after a period of exposure, which includes the application of the cathode potential to the specified surface.
This method can be used in various technological processesin which the metal is in contact with an aqueous solution, in particular, in heat exchangers. The disadvantage of this method is that it does not protect the metal surface from corrosion after removing the cathode potential.
Thus, currently there is a need to develop an improved method for preventing the formation of scale of heating pipes, water-heating and steam boilers, which would be economical and highly efficient and provided anti-corrosion protection of the surface for a long period of time after exposure.
In the present invention, the specified problem is solved using the method according to which there is a current electric potential on a metal surface, sufficient to neutralize the electrostatic component of the adhesion of colloidal particles and ions to a metal surface.
Brief Description of the Invention
The objective of the present invention is to ensure an improved method for preventing the formation of water-heating and steam boilers.
Another objective of the present invention is to ensure the possibility of exclusion or a significant reduction in the need to remove scale during the operation of hot water and steam boilers.
Another object of the present invention is to eliminate the need to use flowable reagents to prevent the formation of scale and corrosion of heating pipes of water-heating and steam boilers.
Another object of the present invention is to ensure the possibility of starting work to prevent the formation of scale and corrosion of heating pipes of hot water and steam boilers on the contaminated pipes of the boiler.
The present invention relates to a method for preventing the formation of scale and corrosion on a metal surface made of iron-containing alloy and in contact with a steam room, which is capable of forming. The specified method is an annex to the specified metal surface of the current electric potential sufficient to neutralize the electrostatic component of the adhesion force of colloidal particles and ions to the metallic surface.
According to some particular embodiments of the claimed method, the current potential is set within 61-150 V. According to some particular embodiments of the claimed method, the above-mentioned iron-containing alloy is steel. In some embodiments, the metallic surface is the inner surface of the heating pipes of the hot water or steam boiler.
The method disclosed in this specification has the following advantages. One advantage of the method is the reduced formation of scale. Another advantage of the present invention is the ability to use once a purchased operating electrophysical apparatus without the need to use consumables synthetic reagents. Another advantage is the possibility of starting work on the contaminated tubes of the boiler.
The technical result of the present invention, therefore, is to increase the efficiency of water and steam boilers, increased productivity, increase the efficiency of heat transfer, reduced fuel consumption for boiler heating, energy savings, etc.
Other technical results and advantages of the present invention include ensuring the possibility of layer-by-layer destruction and removal of the already formed scale, as well as to prevent its new education.
Brief description of the drawings
Figure 1 shows the nature of the distribution of deposits on the inner surfaces of the boiler as a result of the use of the method according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The method according to the present invention is an annex to a metal surface, subject to the formation of scale, a current electric potential for neutralizing the electrostatic component of the adhesion of colloidal particles and ions forming a scale to a metal surface.
The term "current electric potential" in the sense, in which it is used in this application, means an alternating potential that neutralizing the double electric layer on the metal boundary and a steam room containing salts leading to the formation of scale.
As is known to a person skilled in the art, the electrical charge carriers in the metal, slow compared to the main charge carriers of the electron, are the dislocations of its crystal structure, which carry an electric charge and form dislocation currents. Going to the surface of the heating pipes of the boiler, these currents are part of the double electric layer during the formation of scale. The current, electric, pulsating (i.e., variable), the potential initiates the displacement of the electrical charge of dislocations from the metal surface to the ground. In this respect, it is current dislocation currents. As a result of this current electric potential, the double electric layer is destroyed, and the scale gradually decays and goes into boiler water in the form of a sludge that is removed from the boiler during its periodic purges.
Thus, the term "current potential" is understandable for a person skilled in the art and, in addition, known from the prior art (see, for example, patent RU 2128804 C1).
As a device for creating a current electric potential, for example, a device described in RU 2100492 C1 can be used, which includes a converter with a frequency converter and a pulsating potential regulator, as well as an impulse form controller. Detailed description This device is given in RU 2100492 C1. Any other similar device can also be used, as will be understood by a person skilled in the art.
The current electric potential according to the present invention can be applied to any part of the metal surface removed from the base of the boiler. The place of the application is determined by the convenience and / or efficiency of the application of the claimed method. The specialist in this field of technology, using the information disclosed in the present description, and using standard test techniques, will be able to determine the optimal place of the current electric potential.
In some embodiments of the present invention, the electric potential is variable.
The current electric potential according to the present invention can be attached during different periods time. The time of the potential application is determined by the nature and degree of pollution of the metallic surface, the composition of the water used, temperature regime and the peculiarities of the heat engineering device and other factors known to those skilled in the art. The specialist in this field of technology, using the information disclosed in the present description and using standard test techniques, will be able to determine the optimal time of the current electric potential application, based on the purposes, the conditions and state of the heat engineering device.
The magnitude of the current potential required to neutralize the electrostatic component of the adhesion force can be determined by a colloidal chemistry specialist on the basis of information known from the prior art, for example, from the book by Dryagin B.V., Churaev N.V., Muller V.M. "Surface forces", Moscow, Science, 1985. According to some embodiments, the value of the current electric potential is in the range of 10 V to 200 V, more preferably from 60 V to 150 V, even more preferably from 61 V to 150 V. The values \u200b\u200bof the current electric potential in the range from 61 V to 150 V lead to the discharge of a double electric layer, which is the basis of the electrostatic component of the adhesion forces in scale and, as a result, the destruction of scale. The values \u200b\u200bof the current potential are lower than 61 V are insufficient for the destruction of the scale, and with the values \u200b\u200bof the current potential above 150 V is likely the beginning of the unwanted electroerosion destruction of the metal of heating tubes.
The metal surface to which the method according to the present invention can be used can be part of the following heat engineering devices: heating pipes of steam and hot water boilers, heat exchangers, boiler plants, evaporators, heating parts, residential houses and industrial objects in the process of current operation. This list is illustrative and does not limit the list of devices to which the method according to the present invention can be applied.
In some embodiments, the iron-containing alloy from which the metal surface is made to which the method according to the present invention can be applied, may be steel or other iron-containing material, such as cast iron, cowar, fahehral, \u200b\u200btransformer steel, Altern, Magnichene, Alnico, Chromium steel, Invar, etc. This list is illustrative and does not limit the list of iron-containing alloys to which the method according to the present invention can be applied. A specialist in the art on the basis of information known from the prior art will be able to such iron-containing alloys that can be used according to the present invention.
Water environmentFrom which scale is capable of forming, according to some embodiments of the present invention, is a tap water. The aqueous medium can also be water containing dissolved metals compounds. Dissolved metals compounds may be compounds of iron and / or alkaline earth metals. The aqueous medium can also be an aqueous suspension of colloidal particles of iron compounds and / or alkaline earth metals.
The method according to the present invention removes previously formed sediments and serves as an unhappy means of purifying internal surfaces during the operation of the heat engineering device, in the future the non-free mode of its operation. At the same time, the size of the zone, within which the prevention of the formation of scale and corrosion is achieved, significantly exceeds the size of the zone of effective destruction of scale.
The method according to the present invention has the following advantages:
Does not require the use of reagents, i.e. environmentally safe;
Easy to implement, does not require special devices;
Allows you to increase the coefficient of heat transfer and increase the efficiency of the boilers, which significantly affects the economic performance of its work;
It can be used as an addition to the methods used by the methods of water treatment and separately;
Allows you to abandon the processes of softening and deaeration of water, which largely simplifies technological scheme Boiler rooms and makes it possible to significantly reduce costs during construction and operation.
Possible objects of the method can be water boilers, boilers, utilizers, closed systems Heat supply, installations for thermal destruction of sea water, steam mills, etc.
The absence of corrosion destruction, scale formation on the inner surfaces opens up the ability to develop fundamentally new design and layout solutions of the steam boilers of small and medium power. This will allow, due to the intensification of thermal processes, to achieve a significant reduction in the mass and dimensions of steam boilers. Provide a given temperature level of heating surfaces and, therefore, reduce fuel consumption, volume flue gases and reduce their emissions into the atmosphere.
Example implementation
The method declared in the present invention was tested at the Admiraltey shipyard boiler plants and the Red Chemist. It was shown that the method according to the present invention effectively purifies the inner surfaces of the boilers from deposits. During these works, conventional fuel economy was obtained 3-10%, while the scatter of saving values \u200b\u200bis associated with varying degrees of contamination of the internal surfaces of the boilers. The aim of the work was to evaluate the effectiveness of the claimed method to ensure a non-moneyless, non-free mode of operation of steam bootaggers of average power in the conditions of high-quality water treatment, respect for the water-chemical regime and high professional level operation of equipment.
The test of the method declared in the present invention was carried out on a steam boiler number 3 of DCVR 20/13 of the 4th Krasnoselskaya boiler house of the South-Western branch of the State Unitary Enterprise "TEK St. Petersburg". The operation of the boiler unit was carried out in strict accordance with the requirements of regulatory documents. On the boiler there are all necessary means of controlling the parameters of its operation (pressure and consumption of the produced steam, temperature and feed water, the pressure of blowing air and fuel on the burners, discharge in the basic sections of the gas path of the boiler unit). Steam performance boiler was maintained at 18 t / h, steam pressure in the boiler drum - 8.1 ... 8.3 kg / cm 2. Economizer worked in the heat mode. Water of urban water supply was used as the starting water, which corresponded to the requirements of GOST 2874-82 "Drinking water". It should be noted that the number of iron compounds on entering the specified boiler room, as a rule, exceeds regulatory requirements (0.3 mg / l) and is 0.3-0.5 mg / l, which leads to intensive ingrowth of the internal surfaces with ferrous compounds.
Evaluation of the effectiveness of the method was carried out at the state of the internal surfaces of the boiler.
Evaluation of the effect of the method according to the present invention on the state of the internal surfaces of the heating of the boiler unit.
Prior to the start of the test, an internal inspection of the boiler unit was performed and the initial state of the internal surfaces was recorded. Pre-inspection of the boiler was produced at the beginning heating season, a month after its chemical cleaning. As a result of the inspection, it was revealed: on the surface of the drums, solid solid dark brown sediments with paramagnetic properties and consisting, presumably, from iron oxides. The thickness of the deposits was up to 0.4 mm visually. In the visible part of boiling pipes, preferably on the side of the furnace addressed to the furnace, are not solid solid sediments (up to five spots per 100 mm of pipe length with a size of from 2 to 15 mm and a thickness of up to 0.5 mm visually).
The device for creating a current potential described in RU 2100492 C1 was attached at a point (1) to the hatch (2) of the upper drum from the back side of the boiler (see figure 1). The current electric potential was equal to 100 V. The current electric potential was maintained continuously for 1.5 months. At the end of this period, an autopsy of the boiler was made. As a result of the internal examination of the boiler unit, almost complete lack of deposits (not more than 0.1 mm visually) on the surface (3) of the upper and lower drums in the range of 2-2.5 meters (zone (4)) from the drums of the drums (device attachment points To create a current potential (1)). At the removal of 2.5-3.0 m (zone (5)) from deposit luchkov (6), preserved in the form of separate tuberculos (spots) with a thickness of up to 0.3 mm (see figure 1). Further, as it moves to the front, (at a distance of 3.0-3.5 m from the hatches), continuous sediments begin (7) to 0.4 mm visually, i.e. On this distance from the connection point of the device, the effect of a cleaning method according to the present invention practically did not appear. The current electric potential was equal to 100 V. The current electric potential was maintained continuously for 1.5 months. At the end of this period, an autopsy of the boiler was made. As a result of the internal examination of the boiler unit, almost complete lack of deposits (no more than 0.1 mm visually) on the surface of the upper and lower drums within 2-2.5 meters from the drum luchkov (device attachment points to create a current potential) were established. At the removal of 2.5-3.0 m from the hatching of the deposition, in the form of separate tubercles (spots) with a thickness of up to 0.3 mm (see FIG. 1). Next, as we move to the front (at a distance of 3.0-3.5 m from the hatch), continuous deposits begin to 0.4 mm visually, i.e. On this distance from the connection point of the device, the effect of a cleaning method according to the present invention practically did not appear.
In the visible portion of boiling pipes, within 3.5-4.0 m from the drums, there was almost a complete absence of deposits. Next, as it moves to the front, there are not solid solid sediments (up to five spots per 100 pm with a size of from 2 to 15 mm and a thickness of up to 0.5 mm visually).
As a result of this test stage, it was concluded that the method according to the present invention without the use of any reagents makes it possible to effectively destroy previously formed deposits and provides a non-free operation of the boiler.
At the next stage, the test device for creating a current potential was attached at the point "B" and the tests continued for another 30-45 days.
Another opening of the boiler unit was produced after 3.5 months of continuous operation of the device.
An inspection of the boiler unit showed that the remaining sediments were completely destroyed and only in minor quantities were preserved in the lower sections of boiling pipes.
This made it possible to draw the following conclusions:
The size of the zone, within the limits of which the boiler's non-free operation is ensured, significantly exceed the size of the zone of effective destruction of deposits, which allows the subsequent transfer of the point of connection of the current potential to clean the entire inner surface of the boiler unit and further maintain the non-free mode of its operation;
The destruction of previously formed deposits and the prevention of education is provided by various processes in nature.
According to the results of the inspection, it was decided to continue testing to the end heating period In order to finally clean the drums and boiling pipes and clarify the reliability of providing a non-free module of the boiler. Another opening of the boiler unit was produced in 210 days.
The results of the internal inspection of the boiler showed that the process of cleaning the internal surfaces of the boiler within the upper and lower drums and boiling pipes ended with almost complete deletion of deposits. On the entire surface of the metal, a thin dense coating was formed, having a black color with blue party, the thickness of which is even in the moistened state (almost immediately after opening the boiler) did not exceed 0.1 mm visually.
At the same time, the reliability of providing a non-free operation of the boiler unit was confirmed when using the method of the present invention.
The protective effect of the magnetite film was preserved up to 2 months after disconnecting the device, which is enough to ensure the conservation of the boiler unit with a dry way when it is transferred to the reserve or for repair.
Although the present invention has been described in relation to various specific examples and embodiments of the invention, it should be understood that this invention is not limited to them and that it can be implemented in practice within the scope of the claim below
1. A method of preventing the formation of scale on a metal surface made of iron-containing alloy and is in contact with a steam room from which a scale is capable of forming an application to the specified metal surface of the current electric potential in the range from 61 V to 150 V to neutralize the electrostatic component of force Adhesion between the specified metal surface and colloidal particles and ions forming the scale.
The invention relates to thermal power and can be used to protect against scale and corrosion of heating pipes of steam and water boilers, heat exchangers, boiler installations, evaporators, heating parts, residential house heating systems and industrial objects during operation. The method of preventing the formation of scale on a metal surface made of iron-containing alloy and is in contact with a steam room from which scale is capable of forming the application to the specified metal surface of the current electric potential in the range from 61 V to 150 V to neutralize the electrostatic component of the adhesion force between The specified metal surface and colloidal particles and ions that form scale. The technical result is to improve the efficiency and productivity of the operation of hot water and steam boilers, an increase in the efficiency of heat transfer, ensuring layer-by-layer destruction and removal of the resulting scale, as well as the prevention of its new education. 2 Z.P. F-lies, 1 pr., 1 yl.
What is hydro-ix:
Hydro-X (Hydro-X) is called invented invented method and solution invented in Denmark 70 years ago providing the necessary correctional treatment of water for heating systems and boilers of both water heating and steam steam (up to 40 atm). When using the hydro-ix method, only one solution supplied to the consumer in plastic cannors or barrels is already ready for use is added to the circulating water. This allows you to not have in enterprises of special warehouses for chemical reagents, shops for the preparation of the necessary solutions, etc.
The use of hydro-ix ensures that the required pH is maintained, water purification from oxygen and free carbon dioxide, preventing the appearance of scale, and when there is no cleaning of surfaces, as well as corrosion protection.
Hydro-X is a transparent yellowish-brown liquid, homogeneous, strongly alkaline, with a specific weighing of about 1.19 g / cm at 20 ° C. Its composition is stable and even with long-term storage, the separation of fluid or precipitation is not located, so there is no need for stirring before use. Liquid is not flammable.
The advantages of the hydro-ix method are simplicity and efficiency of water treatment.
When operating water heating systems, including heat exchangers, water heating or steam boilers, as a rule, their feeding is made with additional water. To prevent the appearance of scale, it is necessary to carry out water treatment in order to reduce the content of sludge and salts in boiler water. Water treatment can be carried out, for example, through the use of softening filters, desalting, reverse osmosis et al. Even after such treatment, there are problems associated with possible corrosion. When adding caustic soda, trinitium phosphate, etc., the problem of corrosion remains, and for steam boilers and steam pollution.
A fairly simple method that prevents the appearance of scale and corrosion is the hydro-ix method, according to which a small amount of already cooked solution is added to boiler water containing 8 organic and inorganic components. The advantages of the method are as follows:
- The solution enters the consumer in the ready-to-use form;
- Solution B. small quantities introduced into the water or manually, or using the dispenser pump;
- when using Hydro-X, there is no need to apply other chemicals;
- in boiler water is supplied about 10 times less than active substances than when using traditional water treatment methods;
Hydro-X does not contain toxic components. In addition to the sodium hydroxide NaOH and trinitrium phosphate Na3PO4, all other substances are extracted from non-toxic plants;
- When used in steam boilers and evaporators, pure steam is provided and the possibility of foaming is prevented.
The composition of hydro-ix.
The solution includes eight different substances of both organic and inorganic. The mechanism of action of hydro-ix is \u200b\u200ba comprehensive physico-chemical character.
The direction of the effect of each component is approximately the following.
NaOH sodium hydroxide in the amount of 225 g / l reduces the rigidity of water and adjusts the pH value, protects the magnetite layer; Tinodium phosphate Na3PO4 in an amount of 2.25 g / l - prevents the formation of scale and protects the surface of iron. All six organic compounds in the amount do not exceed 50 g / l and include lignin, tannin, starch, glycol, alginate and sodium mannurond. The total number of basic substances NaOH and Na3PO4 during water treatment hydro-ix is \u200b\u200bvery small, about ten times less than used in traditional processing, according to the principle of stoichiometry.
The effect of hydro-ix components is more physical than chemical.
Organic additives serve as the following goals.
Sodium alginate and mannurondate are used together with some catalysts and contribute to the precipitation of calcium and magnesium salts. Tanines absorb oxygen and create a corrosion-protective layer of iron. Lignin acts like Tanin, and also contributes to the removal of the existing scale. Starch forms sludge, and glycol prevents foaming and injuries of moisture drops. Inorganic compounds support the necessary alkaline environment necessary for the effective effect of organic substances, serve as an indicator of the hydro-ix concentration.
Principle of operation of hydro-ix.
The decisive role in the action of hydro-ix is \u200b\u200borganic components. Although they are present in the minimum quantities, due to the deep dispersion, their active reaction surface is large enough. The molecular weight of the organic components of the hydro-ix is \u200b\u200bsignificant, which ensures the physical effect of attracting water pollutants molecules. This stage of water treatment proceeds without chemical reactions. Absorption of pollutant molecules is neutral. This allows you to collect all such molecules as creating rigidity and salts of iron, chlorides, silicic acid salts, etc. All water pollutants are depressed in a slam that is moving, amorphine and does not stick. This prevents the possibility of forming the scale on the heating surfaces, which is the essential advantage of the hydro-ix method.
Neutral hydro-ix molecules are absorbed both positive and negative ions (anions and cations), which in turn are mutually neutralized. Neutralization of ions directly affects the decrease in electrochemical corrosion, since this type of corrosion is associated with different electrical potential.
Hydro-X is effective against corrosion-hazardous gases - oxygen and free carbon dioxide. The concentration of hydro-ix in 10 RRT is quite sufficient to prevent this type of corrosion regardless of the temperature of the medium.
Caustic soda can lead to the appearance of caustic fragility. The use of hydro-ix reduces the number of free hydroxides, significantly reducing the risk of caustic fragility of steel.
Without stopping the system for washing, the hydro-ix process allows you to remove the old existing scale. This is due to the presence of lignin molecules. These molecules penetrate the pores of the boiler scale and destroy it. Although it should still be noted that if the boiler is heavily polluted, it is economically more expedient to conduct a chemical flushing, and then to prevent scale to use Hydro-X, which will reduce its consumption.
The resulting slurry is assembled in the slurry and removed from them by periodic purges. Filters (muds) can be used as a slurry, through which the part of the water returned to the boiler is passed.
It is important that the hydro-ix formed under the action will be removed by daily blowing boiler under the action. The magnitude of the purge depends on the rigidity of water and the type of enterprise. In the initial period, when surfaces are cleaning from the already existing sludge and in the water there is a significant content of pollutants, purge must be greater. Purge is carried out by the full opening of the purge valve for 15-20 seconds daily, and with a large fuel raw water 3-4 times a day.
Hydro-Iks can be used in heating systems, in centralized heat supply systems, for steam boilers of low pressure (up to 3.9 MPa). Simultaneously with the hydro-ix, no other reagents should be used, except sodium sulfite and soda. It goes without saying that reagents for additive water do not belong to this category.
In the first few months of operation, the reagent consumption should be somewhat somewhat, in order to eliminate the existing scale. If there is a fear that the boiler superheater is contaminated with salt deposits, it should be cleaned by other methods.
If there is an external water treatment system, you must select the optimal mode of operation of the hydro-ix, which will ensure common savings.
Overdose Hydro-X does not affect negatively on the reliability of the boiler, nor on the quality of steam boilers and only increase the consumption of the reagent itself.
Steam boilers
As an additive water used raw water.
Permanent dosage: 0.2 liters Hydro-Iks for each meter cubic additive water and 0.04 liters of hydro-ix for each meter cubic condensate.
As an additive water softened water.
Initial dosage: 1 l Hydro-Iks for each meter cubic water in the boiler.
Permanent dosage: 0.04 liters Hydro-Iks for each meter cubic additive water and condensate.
Dosage for cleaning the boiler from scale: Hydro-X is dosed in an amount of 50% more permanent dose.
Heat Systems
As made of water - raw water.
Initial dosage: 1 l Hydro-Iks for each meter cubic water.
Permanent dosage: 1 l Hydro-Iks on each meter cubic feeding water.
As a softener water - softened water.
Initial dosage: 0.5 l Hydro-Iks for each meter cubic water.
Permanent dosage: 0.5 L Hydro-Iks for each meter cubic feeding water.
In practice, additional dosage is based on the results of the pH and rigidity analyzes.
Measurement and control
Normal dosage of hydro-ix is \u200b\u200bapproximately 200-400 ml per day per ton of added water at an average hardness of 350 μg / dm3 per Saco3, plus 40 ml per ton reverse water. This, of course, estimated numbers, and more accurate dosing can be established by the quality control. As already noted, an overdose will not harm, but the correct dosage will save money. For normal operation, stiffness control is carried out (based on Saso3), the total concentration of ionic impurities, specific electrical conductivity, caustic alkalinity, indicator of the concentration of hydrogen ions (pH) of water. Due to the simplicity and large range of reliability, the hydro-ix can be used both by manual dosing and automatic mode. If desired, the consumer can order a system of control and computer management process.
Introduction
Corrosion (from lat. Corrosio - corrosion) is spontaneous destruction of metals as a result of chemical or physico-chemical interaction with environmental. IN general This is the destruction of any material - whether metal or ceramics, wood or polymer. The cause of corrosion is the thermodynamic instability structural materials To the effects of substances that are in contact with them. Example - oxygen corrosion of iron in water:
4Fe + 2N 2 O + ZO 2 \u003d 2 (Fe 2 O 3 H 2 O)
In everyday life for iron alloys (steels), the term "rust" is more often used. Less known cases of corrosion of polymers. In relation to them, there is the concept of "aging", similar to the term "corrosion" for metals. For example, aging rubber due to the interaction with air oxygen or the destruction of some plastics under the influence of atmospheric precipitation, as well as biological corrosion. The rate of corrosion, as well as any chemical reaction, is very dependent on temperature. An increase in temperature per 100 degrees can increase corrosion rate by several orders.
Corrosion processes are distinguished by the widespread and variety of conditions and environments in which it flows. Therefore, there is no single and comprehensive classification of encouraging cases. The main classification is made by the process of proceeding process. Two types are distinguished: chemical corrosion and electrochemical corrosion. In this essay, chemical corrosion is considered in detail on the example of ship boiler installations of small and large capacities.
Corrosion processes are distinguished by the widespread and variety of conditions and environments in which it flows. Therefore, there is no single and comprehensive classification of encouraging cases.
By type of aggressive environments, in which the process of destruction flows, corrosion may be of the following types:
1) -Gazy corrosion
2) -corrosia in non-electrolytes
3) -atmospheric corrosion
4) -corrosion in electrolytes
5) -poded corrosion
6) -Birrosia
7) -Corrosive current.
Under the conditions of the corrosion process, the following types are distinguished:
1) - Contact corrosion
2) -cake corrosion
3) -Corrosion with incomplete immersion
4) - Corrosion with full immersion
5) - Corrosion with variable immersion
6) -crosium with friction
7) - Corrosive stress.
By the nature of destruction:
Solid corrosion covering the entire surface:
1) structural;
2) -News;
3) - Selective.
Local (local) corrosion, covering individual sections:
1) -Paths;
2)-grind;
3) actuator (or pitting);
4) -crying;
5) -Muzhcrystallite.
1. Chemical corrosion
Imagine a metal in the process of producing metal rolled products at a metallurgical plant: a hot mass is moving along the rolling mills. Fire splashes flew away from it. This is from the surface of the metal the particles of the scale - the product of chemical corrosion, resulting from the interaction of the metal with air oxygen. Such a process of spontaneous destruction of the metal due to the immediate interaction of the oxidizer particles and the oxidized metal is called chemical corrosion.
Chemical corrosion - the interaction of the metal surface with (corrosion-active) medium, not accompanied by the occurrence of electrochemical processes on the border of the phases. In this case, the interaction of the metal oxidation and the restoration of the oxidative component of the corrosion environment proceed in one act. For example, the formation of scale in the interaction of iron-based materials at high oxygen temperature:
4Fe + 3O 2 → 2FE 2 O 3
With electrochemical corrosion, the ionization of metal atoms and the reduction of the oxidative component of the corrosion medium proceeds not in one act and their speed depend on the electrode potential of the metal (for example, steel rusting in seawater).
With chemical corrosion, the metal oxidation and the restoration of the oxidative component of the corrosion medium occur simultaneously. Such corrosion is observed under action on the metals of dry gases (air, fuel combustion products) and liquid non-electrolytes (oil, gasoline, etc.) and is a heterogeneous chemical reaction.
The process of chemical corrosion occurs as follows. The oxidative component of the external environment, taking the metal valence electrons, simultaneously comes into a chemical compound with it, forming a film on the surface of the metal (corrosion product). Further formation of the film occurs due to mutual bilateral diffusion through the film of the aggressive medium to the metal and metal atoms towards the external environment and their interaction. At the same time, if the resulting film has protective properties, i.e., it prevents the diffusion of atoms, then corrosion proceeds with self-blocking in time. Such a film is formed on copper at a heating temperature of 100 ° C, on the nickel at 650, at the gland - at 400 ° C. Heating steel products above 600 ° C leads to the formation of a loose film on their surface. With increasing temperature, the oxidation process comes with acceleration.
The most common type of chemical corrosion is the corrosion of metals in gases at high temperatures - gas corrosion. Examples of such corrosion are oxidation of fittings of furnaces, parts of internal combustion engines, grate, parts kerosene lamps and oxidation with high-temperature processing of metals (forging, rolling, stamping). On the surface of metal products, education and other corrosion products are possible. For example, under the action of sulfur compounds on the gland, sulfur compounds are formed, on silver under the action of the iodine vapor - iodide silver, etc. However, a layer of oxide compounds is formed on the surface of the metals.
A large influence on the speed of chemical corrosion has a temperature. With an increase in temperature, the rate of gas corrosion increases. The composition of the gas medium has a specific effect on the rate of corrosion of various metals. So, nickel is stable in the oxygen medium, carbon dioxide, but strongly corps in the atmosphere of sulfur gas. Copper is subject to corrosion in an oxygen atmosphere, but a resistant in the atmosphere of sulfur gas. Chromium has corrosion resistance in all three gas environments.
To protect against gas corrosion, heat-resistant doping of chromium, aluminum and silicon, the creation of protective atmospheres and protective coatings by aluminum, chromium, silicon and heat-resistant enamels.
2. Chemical corrosion in ship steam boilers.
Types of corrosion. In the process of operation, elements of the steam boiler are exposed to aggressive medium - water, steam and flue gases. Corrosive chemical and electrochemical.
Chemical corrosion are subject to parts and nodes of machines operating at high temperatures- Piston and turbine type engines, rocket engines, etc. The chemical affinity of most metals to oxygen at high temperatures is almost unlimited, since all technically important metal oxides are able to dissolve in metals and returned from the equilibrium system:
2ME (T) + O 2 (d) 2ME (T); Meo (T) [MoO] (R-R)Under these conditions, oxidation is always possible, but along with the dissolution of the oxide, an oxide layer appears on the metal surface, which can slow down the oxidation process.
The speed of metal oxidation depends on the speed of the chemical reaction itself and the rate of diffusion of the oxidant through the film, and therefore protective action The films are the higher, the better its continuity and below diffusion ability. The continuity of the film formed on the surface of the metal can be estimated with respect to the volume of the formation of oxide or other any compound to the volume of metal consumed on the formation of this oxide (Pulling-Badwards factor). The coefficient A (Pulling - Badwards factor) in different metals has different meanings. Metals, which a<1, не могут создавать сплошные оксидные слои, и через несплошности в слое (трещины) кислород свободно проникает к поверхности металла.
Solid and stable oxide layers are formed at a = 1.2-1.6, but at high values \u200b\u200bof a film, the films are obtained uninstalled, easily separated from the metal surface (iron scale) as a result of emerging internal stresses.
Pilling - Badwards factor gives a very approximate estimate, since the composition of the oxide layers has a greater latitude of the homogeneity region, which is reflected in the oxide density. So, for example, for chromium a = 2.02 (according to pure phases), but the oxide film generated on it is very resistant to environmental action. The thickness of the oxide film on the metal surface varies depending on the time.
Chemical corrosion caused by steam or water destroys the metal evenly over the entire surface. The speed of such corrosion in modern ship boilers is low. Local chemical corrosion caused by aggressive chemical compounds contained in the sediments of ash (sulfur, vanadium oxides, etc.).
Electrochemical corrosion, as its name shows, is associated not only with chemical processes, but also with the movement of electrons in interacting media, i.e. With the advent of electric current. These processes occur in the interaction of metal with electrolyte solutions, which takes place in a steam boiler in which the boiler water is circulating, which is a solution of salts and alkalis. Electrochemical corrosion also proceeds in contact with air (at normal temperature), containing always a pair of water, which condensed on the metal surface in the form of the finest moisture film, create conditions for the flow of electrochemical corrosion.
Accidents of steam boilers associated with violation of water regime, corrosion and metal erosion
Normal water regime is one of the most important conditions for the reliability and efficiency of the operation of the boiler installation. The use of water with increased rigidity to feed boilers entails the formation of scale, fuel consumption and increase the cost of repair and cleaning boilers. It is known that the scale formation can lead to a steam boiler accident due to the heating surfaces. Therefore, the correct water regime in the boiler room should be considered not only from the point of view of increasing the cost-effectiveness of the boiler room installation, but also as the most important prophylactic event to combat accidents.
Currently, the boiler plants of industrial enterprises are equipped with water preparatory devices, so the conditions for their operation have improved and the number of accidents caused by scale formation and corrosion significantly decreased.
However, in some enterprises, the administration formally fulfilling the requirement of the Cottal Control rules on the equipment of boilers by water-opticians does not provide normal operating conditions of these settings, does not control the quality of the nutrient water and the condition of the heat heating surfaces, allowing the contamination of boilers with screaming and sludge. We give several examples of accidents of boilers for these reasons.
1. In the boiler plant of precast concrete structures due to violations of the water regime in the DKVR-6 boiler, 5-13 there was a breakdown of three screen pipes, part of the on-screen pipes was deformed, foils were formed on many pipes.
In the boiler room there is a two-stage sodium-cationic water purification and a deaerator, but the normal operation of water preparation equipment did not pay due attention. The regeneration of ka-thionite filters was not carried out in the deadlines established by the instructions, the quality of the nutrient and boiler water was rarely checked, the periodic reverging of the boiler was not observed. The water in the deaerator did not heal to the dark of the temperature and therefore the waterticination of the water did not actually happen.
It was also established that the boiler was often served with raw water, and the requirements of "rules of device and safe operation of steam and water boilers" did not comply with the requirements of which the locking organs on the raw water line should be sealing in the closed position, and each raw water failure should To be recorded in the journal of water treatment. From individual records in the water treatment journal, it can be seen that the rigidity of the nutrient water reached 2 mG-eq / kg and more, with a 0.02 mg-eq / kg permissible on the standards. Most often, such entries were made in the magazine: "Water dirty, rigid", without indicating the results of chemical analysis of water.
When viewing the boiler after stopping on the inner surfaces of the screen pipes, deposits to 5 mm thick were detected, separate pipes are almost completely clogged with screaming and sludge. On the inner surface of the drum in the lower part, the thickness of the deposits reached 3 mm, the front of the drum one third in height is littered with sludge.
For 11 months Prior to this accident, similar damage ("cracks, dewins, deformation) were identified in the 13-screen boiler pipes. The defective pipes were replaced, but the administration of the PRESIDATION in violation of the "Instructions for the Investigation of accidents, but entailed accidents on enterprises under control of the Gosgor, the Thams of enterprises and facilities" did not investigate this case and did not take measures to improve the operating conditions of the boilers.
2. At the energy output, it is raw water to supply a single-altered water-tube shielded steam boiler with a capacity of 10 t / h with a working pressure of 41 kgf / cm2 was treated by the method of cation exchange. Due to the unsatisfactory work, the cation and the novel filter residual stiffness of the softened water reached
0.7 mG-eq / kg Instead of the provided for by the draft 0.01 MG-EC / kg. About the paddling of the boiler was carried out irregularly. When stopping for repair, the boiler boiler and screenshots were not opened and did not look at. Due to the deposits of scale, there was a break of the pipe, while the ferry and burning fuel, thrown out of the furnace, a fireman was burned.
The accident could not be if the boiler's coaching door was closed on a cheek, how the rules for the self-operation of boilers are required.
3. The newly mounted one drum water tube boiler with a capacity of 35 t / h with a working pressure of 43 kgf / cm2 was put into operation at the cement plant, the installation of which was not completed by this time. During the month, the boiler was powered by crude water. The water deaeration was not produced for more than two months, since steamer was not connected to the deaerator.
Disorders of the water regime were allowed after in. Adoped manufacturing equipment was included in the work. The boiler was often fueled with raw water; The purge mode was not observed; The chemical laboratory did not control the quality of the nutrient water, since it was not equipped with the necessary reagents.
Due to the unsatisfactory water of the deposit on the internal surfaces of the on-screen pipes, 8 mm thickness reached; As a result, foils were formed on 36 on-screen pipes. A significant part of the pipes was deformed, the walls of the drum on the inside were corrosion.
4. At the factory of reinforced concrete products, the power boiler of the Shukhov-Berlin system was produced by water treated with an electromagnetic manner. It is known that with the method of water treatment, the timely spectacular removal of the sludge from the boiler should be ensured.
However, during the operation of the boiler, this condition was not performed. The blowing of the boiler was carried out irregularly, the schedule of stopping the boiler on the flushing and cleaning was not respected.
In the result, a large amount of sludge accumulated inside the boiler. The back of the pipes was clogged with sludge at 70-80% of the section, the mud - by 70% of the volume, the thickness of the scale on the heating surfaces reached 4 mm. This led to overheating and deformations of boiling pipes, tube RSSchka and tubular sections heads.
When choosing an electromagnetic method of processing iodine in this case, the quality of nutrient water and the design features of the boiler did not take into account, and measures were taken to organize a normal purge mode, which led to the accumulation of sludge and significant deposits of scale in the boiler.
5. Exceptional importance has acquired the issues of organizing a rational water regime to ensure reliable and economical operation of heat power plates.
The formation of deposits on the surfaces of the heating of boiler aggregates occurs as a result of complex physicochemical processes in which not only calcifies are involved, but also metal oxides and easily soluble compounds. Dealers of sediments shows that along with salt-forming salts, they contain a significant amount of iron oxides, which are products of corrosion processes.
Over the past years, significant successes have been achieved in our country in organizing a rational water regime of heat power plants and chemical water control and ferry, as well as in the introduction of corrosion-resistant metals and protective coatings.
The use of modern water treatment facilities made it possible to sharply improve the reliability and efficiency of the operation of the energy equipment.
However, water regime disorders are still allowed on separate thermal power plants.
In June 1976, for this reason, an accident occurred at the CHP of the pulp and paper plant on a steam boiler of the BKZ-220-100 F tubing capacity of 220 t / h with a pair of 100 kgf / cm2 and 540 ° C parameters made on the Barnaul Kotel-Building Plant in 1964 G. The boiler is single-backed with natural circulation, made according to the P-shaped scheme. The coaching chamber prismatic is completely shielded with pipes with an outer diameter of 60 mm, the step of which is 64 mm. The lower part of the on-screen surface forms the so-called cold funnel, according to the slopes of which the particles of the slag in solid form are rolled down into the slag chest. The diagram of evaporation of two-stage, washing a pair of nutrient water. The first stage of evaporation is included directly into the boiler drum, the second step is the remote paosnel cyclones included in the circuit circulation of the middle side screen blocks.
The power supply of the boiler is carried out with a mixture of chemically purified water (60%) and condensate coming from turbines and industrial workshops (40%). Water for powering the boiler is processed according to the scheme: Lime - Coagulation - Magnezial Exploring in
Lighters - two-stage cationing.
The boiler operates at the angle of an asterian field with a relatively low ash melting point. Masout is used as a cast fuel. Before the accident, the boiler worked 73,300 h.
On the day of the accident, the boiler was included at 00 h 45 min and worked without deviating from a normal mode to 14 hours. The pressure in the drum for this period of operation was maintained within 84-102 kgf / cm2, the steam consumption was 145-180 t / h, temperature superheated steam-520-535 ° C.
At 14 h 10 min there was a gap of 11 front-screen pipes in a cold funnel zone at 3.7 m with partial destruction
cutting. It is assumed that first there was a gap of aquatic or two pipes, and then followed the rupture of the remaining pipes. The water level dropped sharply, and the boiler was stopped by automatic protection.
Inspection showed that inclined areas of cold funnel pipes were destroyed outside flexible, and two pipes were torn off from the first front bottom manifold from the second-nine. The gap is fragile, the edges in the breakdown places are stupid and do not have thinning. The length of the broken pieces of pipes is from one to three meters. On the inner surface of damaged pipes, as well as samples cut from intact pipes, loose deposits with a thickness of up to 2.5 mm, as well as a large number of yazvin, a depth of 2 mm, located in a chain of up to 10 mm wide by two pipe heating along the border of the pipe heating. It was in places of corrosion damage that the metal destruction occurred.
During the investigation of the accident, it turned out that earlier in the process of operation of the boiler was already the gaps of screen pipes. For example, two months before the accident, the front-screen pipe was ruptured at a mark of 6.0 m. After 3 days, the boiler was again stopped due to the rupture of two front-screen pipes at a mark of 7.0 m. And in these cases, the destruction of pipes was appeared The result of corrosion metal damage.
In accordance with the approved schedule, the boiler should have been stopped for overhaul in the third quarter of 1976. During the repair period, it was planned to replace the front-screen pipes in the cold funnel area. However, the boiler did not stop for repair, and the pipes were not replaced.
Corrosion damage to the metal was consequence of water violations that allowed for a long time during the operation of the CHP boilers. The boilers were powered by water with an elevated content of iron, copper and oxygen. The total content of salts in nutrient water significantly exceeded the permissible norms, as a result of which, even in the contours of the first stage of evaporation, the salt content of salts reached 800 mg / kg. Production condensates used to feed boilers with iron content of 400-600 mg / kg did not purify. For this reason, as well as due to the fact that there was no sufficient anticorrosive protection of water preparatory equipment (protection was carried out in part), there were significant deposits on the internal surfaces of the pipes (up to 1000 g / m2), mainly consisting of iron compounds. The amination and hydra-zinning of nutritious water was introduced only shortly before the accident. Preparation and operational acid flushing boilers were not produced.
The emergence of the accident also contributed to other violations of the rules for the technical operation of boilers. At the CHP very often calmed boilers, and the greatest number of extras accounted for the boiler with which an accident occurred. The boilers are equipped with steam heating devices, but they did not use them during the crossing. During extras, they did not control the movement of screen collectors.
To clarify the nature of the corrosion process and clarify the reasons for the formation of Yazvin mainly in the first two panels of the front screen and the location of these Yazvin in the form of chains, the cases of the accident investigation were sent to the CCT. When considering these materials, attention was drawn to the fact that
the boilers worked with a sharp variable load, while a significant decrease in the steam output (up to 90 t / h) was allowed, in which the local circulation disorder is possible. The boilers were melted in the following way: at the beginning, the extras included two nozzles, located on the diagonal (diagonally). This method led to a slowdown in the process of natural circulation in the panels of the first and second front screens. It is in these screens and found the main focus of ulcerative damage. In the nutrient water, nitrites appeared episodically, for the concentration of which the control was not carried out.
Analysis of the materials of the accident, taking into account the following deficiencies, gave reason to believe that the formation of the yazvin chains on the side-forming internal surfaces of the front-screen pipes on the cold funnel's skate is the result of a long process of submissive electrochemical corrosion. The depolarizers of this process were nitrites and dissolved in water oxygen.
The location of the yazvin in the form of chains is, apparently, the result of the operation of the boiler during extras with the unsteady process of natural circulation. During the period of the beginning of the circulation on the upper generation of inclined pipes of the cold funnel, pore bubbles are periodically formed, which cause the effect of local thermal populations in metal £ with the flow of electrochemical processes in the library of the phase temporary partition. It was these places that were foci of the formation of chains of Yazvin. The predominant formation of Yazvin in the first twist of the front-screen panels was due to the wrong mode of the extract.
6. In the TETS WB, the time of operation of the PC-Yush-2 boiler is 230 t / h with pair-100 kgf parameters / cm2 and 540 ° C, a wiping was noticed on the discharge from the premium collector of fresh steam to the main safety valve. The removal is connected by welding with a cast tee, welded in the collector.
The boiler was emergency stopped. When inspection, the annular crack was detected at the bottom of the pipe (168x13 mm) of the horizontal portion of the outlet in the immediate vicinity of the tap attachment site to the cast tee. The length of the crack on the outer surface is 70 mm and on the inner surface-110 mm. On the inner surface of the pipe, a large number of corrosion yazvin and individual cracks located in parallel are revealed on its injury.
Metallographic analysis establishes that cracks begin from Yazvin in a metal-led metal layer and further develop transcrystallinically in the direction perpendicular to the surface of the pipe. Metal microstructure Pipes - ferrite grains and thin pearlity chains on grain boundaries. On a scale given in the form of annex to MRTU 14-4-21-67, the microstructure can be estimated by a score of 8.
The chemical composition of the metal damaged pipe corresponds to the steel 12x1mf. Mechanical properties meet the requirements of technical specifications. The diameter of the pipe on the damaged area does not go beyond the limits of the plus tolerance.
Horizontal removal to the safety valve with an unregulated mounting system can be considered as a console beam, welded to a tower rigidly fixed in the collector, with maximum bending stresses at the place of the seal, i.e. in the zone where the pipe has been damaged. With absence
drainage in the discharge and availability of counterclockwise, due to the elastic bending on the site from the safety valve to the collection collector of fresh steam, at the bottom of the pipe in front of the tee, it is possible to constantly accumulate a small amount of condensate, enriched during stops, conservation and boiler starts to work, oxygen From the air. Under these conditions, there was a corrosion corrosion of the metal, and the joint effect on the metal condensation and tensile stress caused its corrosion cracking. During operation in places of corrosion yazvin and shallow cracks as a result of the aggressive impact of medium and variable stresses in the metal, fatigue-corrosion cracks may develop, which, apparently, occurred in this case.
In order for the condensate to be accumulated, the reverse circulation of steam was made in the discharge. For this, the discharge pipe immediately before the main safety valve was connected to the heating line (pipes with a diameter of 10 mm) with an intermediate chamber of the steam-steerlers, according to which steam is supplied with a temperature of 430 ° C. With a small overpressure drop (up to 4 kgf / cm2), a continuous consumption of steam is ensured And the temperature of the medium in the discharge is maintained at no lower than 400 ° C. Reconstruction of the removal was carried out on all PC-Yush-2 CHP boilers.
In order to prevent damage to the taps to the main safety valves on PC-Yush-2 boilers and it is recommended:
Check the lower semitimeters of pipes of taps in welding places for tees;
Check whether the required slopes are met and, if necessary, adjust the steering systems for the main safety valves, taking into account the actual state of the steam pipeline (insulation weight, the actual weight of pipes, former reconstructions);
Make in the taps to the main safety valves inverse steam circulation; The design and inner diameter of the heating steaming in each individual case must be coordinated with the equipment manufacturer;
All dead-end taps for safety valves thoroughly insulate.
(From the express information of the SCRTI OrGRES- 1975)
Corrosion phenomena in boilers are most often manifested on the inner heat-stressed surface and relatively less - on the outer.
In the latter case, metal destruction is due - in most cases, the joint action of corrosion and erosion, which sometimes has the predominant value.
An external sign of erosion destruction is a clean surface of the metal. With the corrosion exposure, corrosion products are usually preserved on its surface.
Internal (in aqueous medium) Corrosion and scale processes can exacerbate the outer corrosion (in the gas environment) due to the thermal resistance of the layer of scale and corrosion deposits, and, consequently, the temperature growth on the metal surface.
The outer corrosion of the metal (from the firebox of the boiler) depends on different factors, but, first of all, from the type and composition of the combed fuel.
Corrosion of gas-fledged boilers
The fuel oil contains organic compounds of vanadium and sodium. If the molten slag deposition containing the compound of vanadium (V) accumulate on the wall of the pipe containing the vanadium compounds (V), then with a large excess of air and / or the surface temperature of the metal 520-880, reactions occur:
4Fe + 3V2O5 \u003d 2Fe2O3 + 3V2O3 (1)
V2O3 + O2 \u003d V2O5 (2)
Fe2O3 + V2O5 \u003d 2FEVO4 (3)
7Fe + 8FeVO4 \u003d 5Fe3O4 + 4V2O3 (4)
(Sodium compounds) + O2 \u003d Na2O (5)
Another corrosion mechanism with the participation of vanadium (liquid eutectic mixture is possible:
2NA2O. V2O4. 5V2O5 + O2 \u003d 2NA2O. 6V2O5 (6)
Na2o. 6V2O5 + M \u003d Na2O. V2O4. 5V2O5 + Mo (7)
(M - Metal)
Vanadium and sodium compounds when combustion of fuel are oxidized to V2O5 and Na2O. In sediments sticking to the metal surface, Na2O is a binder. The liquid formed as a result of the reactions (1) - (7) melts the protective film of magnetite (Fe3O4), which leads to the oxidation of the metal under deposits (the temperature of melting the deposits (slag) - 590-880 OS).
As a result of the indicated processes of the wall of the screen pipes facing the furnace, are evenly thinned.
The growth of metal temperature in which vanadium compounds become liquid, contribute to internal precipitation in the pipes. And thus, when the temperature of the metal flow rate is reached, the pipe rupture occurs - a consequence of the joint action of external and internal deposits.
Corroduces and details of the fastening of pipe screens, as well as protrusions of pipe welds - the rise in temperature on their surface is accelerated: they are not cooled with a steam mixture, like pipes.
The fuel oil may contain (2.0-3.5%) in the form of organic compounds, elementary sulfur, sodium sulfate (Na2SO4) falling into oil from reservoir water. On the surface of the metal in such conditions, vanadium corrosion is accompanied by sulphide-oxide. Their joint action is mostly manifested when there are 87% V2O5 and 13% Na2SO4 in sediments, which corresponds to the content in the fuel oil vanadium and sodium in the 13/1 ratio.
In winter, when heated fuel oil with steam in tanks (to relieve drain), water in the amount of 0.5-5.0% additionally falls into it. Corollary: the amount of deposits on the low-temperature surfaces of the boiler increases, and, obviously, corrosion of mazutoprovods and fuel oil containers are growing.
In addition to the above-described scheme for the destruction of the on-screen pipes of boilers, corrosion of steam-steerlers, fester pipes, boiling beams, economizers have some features due to elevated - in some sections - velocities of gases, especially those containing unburned fuel oil particles and detached slag particles.
Identification of corrosion
The outer surface of the pipes is covered with a dense enhaid layer of sediments of gray and dark gray. On the side facing the firebox, the thinning of the pipe: flat areas and shallow cracks in the form of "rice" are clearly visible if we clean the surface from deposits and oxide films.
If the pipe is emergency destroyed, then a cross-cutting longitudinal non-screed crack is visible.
Corrosion of deductible boilers
In corrosion formed by the action of coal burning products, sulfur and its compounds are determined value. In addition, chlorides (mainly NaCl) and alkali metal compounds affect corrosion processes. The most likely corrosion in the content of more than 3.5% sulfur in the corner and 0.25% chlorine.
Bat ash, containing alkaline compounds and sulfur oxides, is retained on the surface of the metal at a temperature of 560-730 OS. At the same time, alkaline sulfates are formed as a result of occurring reactions, for example, K3FE (SO4) 3 and Na3Fe (SO4) 3. This melted slag, in turn, destroys (melts) a protective oxide layer on metal - magnetite (Fe3O4).
The corrosion rate is maximum at a metal temperature of 680-730 OS, with its increase, the rate decreases due to thermal decomposition of corrosive substances.
The greatest corrosion is in the outlet pipes of the superheater, where the highest pair temperature.
Identification of corrosion
On the on-screen pipes, you can observe flat areas on both sides of the pipe exposed to corrosion destruction. These areas are arranged at an angle of each other 30-45 OS and covered with a layer of deposits. Between them - relatively "clean" plot subjected to the "frontal" effects of the gas flow.
Deposits consist of three layers: an external - porous bat, an intermediate layer - whitish water-soluble alkaline sulfates, inner layer - shiny black iron oxides (Fe3O4) and sulfides (FES).
On low-temperature parts of boilers - economizer, air heater, exhaust fan - metal temperature drops below the "point of dew" of sulfuric acid.
When burning solid fuel, the gas temperature decreases from 1650 OS in a torch to 120 ° C and less in the chimney.
Due to the cooling of the gases, sulfuric acid is formed in the vapor phase, and when contacting the coolest metal surface, the pairs are condensed to the formation of liquid sulfuric acid. The "dew point" of sulfuric acid - 115-170 OS (maybe more - depends on the content in the gas flow of water vapor and sulfur oxide (SO3)).
The process is described by reactions:
S + O2 \u003d SO2 (8)
SO3 + H2O \u003d H2SO4 (9)
H2SO4 + FE \u003d FESO4 + H2 (10)
In the presence of iron and vanadium oxides, the SO3 catalytic oxidation is possible:
2SO2 + O2 \u003d 2SO3 (11)
In some cases, sulfuric acid corrosion when burning coal is less significant than when burning brown, slate, peat and even natural gas - due to relatively greater release of water vapor of them.
Identification of corrosion
This type of corrosion causes uniform destruction of the metal. Typically, the surface is rough, with a small rust raid, and looks like a surface without corrosion phenomena. With prolonged exposure, the metal can be covered by deposits of corrosion products that need to be taken carefully during the examination.
Corrosion during interruptions in operation
This type of corrosion manifests itself on an economizer and in those places of the boiler, where the outer surfaces are covered with sulfur compounds. When cooled boiler, the metal temperature drops below the "dew point" and, as described above, if there are sulfur sediments, sulfuric acid is formed. It is possible an intermediate compound - sulfuric acid (H2SO3), but it is very unstable and immediately turns into sulfuric acid.
Identification of corrosion
Metal surfaces are usually covered with appliances. If you delete them, then the metal destruction areas are found, where sulfur sediments and unquarified metal sections were found. Such an appearance is distinguished by corrosion on a stopped boiler from the above-described corrosion of the economizer metal and other "cold" parts of the working boiler.
When the boiler washed, the corrosion phenomena are distributed more or less evenly on the metal surface due to the erosion of sulfurous sediments and insufficient dry drying. With an insufficient washing, corrosion is localized where there were sulfur compounds.
Metal erosion
Under certain conditions, different boiler systems are subjected to erosion metal destruction under certain conditions, both from the inner and the outer side of the heated metal, and where turbulent flows at high speed occur.
Below is only the erosion of turbines.
Turbines are exposed to erosion from severe particles and droplets of steam condensate. Solid particles (oxides) are peeled from the inner surface of steps and steam pipelines, especially in the conditions of transitional thermal processes.
Condensate Condensate Droplets mainly destroy the surface of the vanes of the last stage of the turbine and drainage pipelines. It is possible a steam condensate erosion-corrosion, if the condensate "sour" - pH is below five units. Corrosion is also hazardous in the presence of a pair of chlorides in water droplets (up to 12% of the mass of deposits) and caustic soda.
Identification of erosion
The destruction of the metal from the blows of the condensate droplets is most noticeable on the front edges of the turbine blades. The edges are covered with thin transverse teeth and grooves (grooves), there may be sloping conical protrusions aimed in the direction of shocks. The protrusions are on the front edges of the blades and are almost absent on their rear planes.
Damage from solid particles have the form of breaks, micro-died and jar on the front edges of the blades. The grooves and inclined cones are absent.
