Foreign technology. Preventing corrosion and scale in closed heat supply systems, hot water and steam boilers. Corrosion damage to the on-screen pipes of gas-contained boilers causes the occurrence of electrochemical corrosion in hot water boilers

For the first time, the outer corrosion of the screen pipes was found at two power plants in high-pressure boilers TP-230-2, who worked on the AC and sulfur coal and sulfur fuel oil and were in operation of about 4 years. The outer surface of the pipes was subjected to corrosion corrosion from the side facing the furnace in the zone of the maximum temperature of the torch. 88.

Mainly destroyed pipes of the middle (width) part of the furnace, directly above the incendiary. belt. Wide and relatively shallow corrosion ulcers had an irregular shape and often closed each other, as a result of which the damaged surface of the pipe was uneven, buggy. In the middle of the deepest ulcers, fistulas appeared, and through them jets of water and steam began to escape.

It was characteristic of the complete absence of such corrosion on the on-screen pipes of the average pressure boilers of these power plants, although medium pressure was there in operation significantly "for a longer time.

In subsequent years, the outer corrosion of the on-screen pipes appeared on other high-pressure boilers worked on solid fuel. The zone of corrosion destruction spread sometimes at a considerable height; In some places, the thickness of the pipe walls as a result of corrosion decreased to 2-3 mm. It was also observed that this corrosion is practically absent in high-pressure boilers working on fuel oil.

The outer corrosion of the on-screen pipes was found in the boilers of TP-240-1 after 4 years of operation working at a pressure of 185 at the drums. In these boilers, the suburbs of brown coal, having humidity of about 30%; The fuel oil was burned only during crossing. These boilers have corrosion destruction also arose in the zone of the highest heat load of the screen pipes. The peculiarity of the corrosion process was that the pipes were destroyed both from the side facing the furnace and from the side facing the smelting (Fig. 62).

These facts show that the corrosion of the on-screen pipes depends primarily on the temperature of their surface. In the mid-pressure boilers, water evaporates at a temperature of about 240 ° C; In boilers, calculated on the pressure of 110 AT, the estimated boiling point of water is 317 ° C; In TP-240-1 boilers, water boils at a temperature of 358 ° C. The temperature of the outer surface of the screen pipes usually exceeds the boiling point of about 30-40 ° C.

Can. Assuming that intensive outer corrosion of the metal begins with an increase in its temperature to 350 ° C. In the boilers designed for pressure 110 AT, this temperature is achieved only with the firing side of the pipes, and in boilers having a pressure of 185 AT, it corresponds to water temperature in pipes . That is why the corrosion of the on-screen pipes by the clutch was observed only in these boilers.

A detailed study of the issue was produced at TP-230-2 boilers working on one of the above-mentioned power plants. There were taken samples of gases and hot

A torch particles from a torch at a distance of about 25 mm from the on-screen pipes. Near the front screen in the zone of intense outer corrosion of pipes, the furnace gases almost did not contain free oxygen. Near the rear screen, in which the outer corrosion of the pipes was almost absent, free oxygen in the gases was significantly more. In addition, the test showed that in the area of \u200b\u200bcorrosion education, more than 70% of the samples of gases

It is possible to "assume that in the presence of excess oxygen, hydrogen sulfide burns and corrosion does not occur, but in the absence of excess oxygen, hydrogen sulfide enters into a chemical connection with the metal of the pipes. At the same time, iron sulfide FES is formed. This corrosion product was indeed found in sediments on screen pipes.

Outdoor corrosion is subject not only carbon steel, but also chromolibdden. In particular, in boilers TP-240-1 corrosion struck onto the on-screen pipes made of steel brands 15xm.

There are still no proven activities for a complete prevention of the described type of corrosion. Some decrease in the speed of destruction. Metal was achieved. After adjusting the combustion process, in particular with an increase in the excess air in the furnace gases.

27. Corrosion of screens for ultrahigh pressure

In this book, briefly described on the conditions of metal of steam boilers of modern power plants. But the progress of energy in the USSR continues, and now a large number of new boilers are built, designed for higher pressure and pair temperature. Under these conditions, the practical experience of operation of several TP-240-1 boilers operating from 1953-1955 is of great importance. With a pressure of 175 at (185 AT in the drum). Very valuable,\u003e in particular, information about corrosion of their screens.

The screens of these boilers were subject to corrosion both with outdoor and inner side. Their external corrosion is described in the previous paragraph of this chapter, the destruction of the inner surface of the pipes does not seem to be one of the types of metal corrosion described above

The corrosion occurred mainly from the fire side of the upper part of the inclined pipes of the cold funnel and was accompanied by the appearance of corrosion sinks (Fig. 63, a). In the future, the number of such shells increased, and a solid strip occurred (sometimes two parallel. Bands) of the metal (Fig. 63,6). The absence of corrosion in the welded joint zone was also characteristic.

Inside the pipes there was a flip of loose sludge with a thickness of 0.1-0.2 mm, which consisted mainly of iron and copper oxides. The increase in the corrosion destruction of the metal was not accompanied by an increase in the thickness of the sludge layer, therefore, corrosion under the layer of the sludge was not the main cause of corrosion of the inner surface of the on-screen pipes.

In boiler water, a clean-phosphate alkalinity mode was maintained. Phosphates were introduced into the boiler is not. It is not possible, and periodically.

The fact that the temperature of the metal pipe temperature is periodically sharply, and sometimes it was above 600 ° C (Fig. 64). The zone of the most frequent and maximum temperature increase coincided with the zone of the greatest destruction of the metal. Reducing the pressure in the boiler up to 140-165 AT (i.e., before the pressure in which new serial boilers operate) did not change the nature of the temporary increase in the temperature of the pipes, but was accompanied by a significant decrease in the maximum value of this temperature. The reasons for such a periodic increase in the temperature of the fire side of the inclined pipes are cold. The funnels have not been studied in detail.

This book discusses specific issues related to the work of steel parts of the steam boiler. But to study these purely practical issues, it is necessary to know the general information relating to the structure of steel and its "properties. In the schemes showing the structure of metals, atoms are sometimes depicted in the form of contacts in contact with each other (Fig. 1). Such schemes show the alignment of atoms in the metal But it is difficult to clearly show the location of the atoms relative to each other. Erosion is the gradual destruction of the metal surface layer under the influence of mechanical exposure. The most common type of erosion of steel elements - a steam boiler is their abrasion of solid ash particles moving along with smoke gases. With long abrasion, there is a gradual decrease in the thickness of the walls of pipes, and then their deformation and gap under the action of internal pressure.

The most active corrosion of the screen tubes is manifested in places concentrating the impurities of the coolant. This includes areas of screen pipes with high heat loads, where there is a deep evaporation of the boiler water (especially in the presence of porous depths on the evaporative surface). Therefore, in relation to the prevention of damage to the on-screen pipes associated with the internal corrosion of the metal, it is necessary to take into account the need for an integrated approach, i.e. Impact both on water-chemical and flue mode.

Damage to the on-screen pipes are mainly mixed, they can be divided into two groups:

1) Damage with signs of overheating steel (deformation and thinning of pipe walls at the destroyer; the presence of graphite grains, etc.).

2) fragile destruction without characteristic signs of overheating of metal.

On the inner surface of many pipes, significant two-layer deposits are marked: the upper - weakly sleeve, the lower - the scale-shaped, tightly adhesive with the metal. The thickness of the lower layer of the scale is 0.4-0.75 mm. In the zone of damage to the scale on the inner surface is destroyed. Near the destroyers and at some distance from them the inner surface of the pipes is amazed by corrosion yazvinas and fragile micro-gras.

The general type of damage indicates a thermal nature of destruction. Structural changes on the front side of the pipes - deep spheridation and the decay of the perlite, graphite formation (carbon transition to graphite 45-85%) - indicates the exceedment not only the operating temperature of the screens, but also permissible for steel 20,500 OS. The presence of FEO also confirms the high level of metal temperatures during operation (above 845 OK - i.e. 572 OS).

Fragile damage caused by hydrogen usually occur in areas with powerful heat fluxes, under thick layers of sediments, and on-clone or horizontal pipes, as well as in the heat transfer sites next to the welds of welds or another to the device, which prevent the free movement of streams. . Experience showed that damage caused by hydrogen occur in boilers under pressure below 1000 ps. inch (6.9 MPa).

Damaged under the action of hydrogen usually lead to ruptures with tol-solar edges. Other mechanisms that contribute to the formation of a wagon-grade with thick edges are corrosion cracking under strokes, corrosion fatigue, breaks under the action of stresses, as well as (in some rare cases) the strongest overheating. It may be per challenging visually distinguishing the destruction caused by hydrogen damage, from other types of destruction, but here they can help the non-their features.

For example, hydrogen damage is almost always associated with the formation of shells in the metal (see the precautionary measures given in G-WAX 4 and 6). Other types of destruction (except, possibly corrosive fatigue, which often begins in separate sinks) usually not related to severe corrosion.

Pipe accidents as a result of hydrogen damage to the metal are often pro-are in the form of education in the wall of the pipe of the rectangular "window", which is not typical for other types of destruction.

To estimate the damage to the screen pipes, it should be borne in mind that the metallurgical (initial) content of hydrogen gaseous hydrogen in steel perlit class (including Article 20) does not exceed 0.5--1 cm3 / 100g. When hydrogen content above 4--5 cm3 / 100g, the mechanical properties of the steel deteriorate significantly. In this case, it is necessary to focus mainly on the local content of residual hydrogen, since in the fragile destruction of the screen pipes, the sharp deterioration in the properties of the metal is observed only in the narrow zone in cross section of the pipe with the consistently satisfactory structure and the mechanical properties of the adjaceable metal at the removal of only 0.2-2 mm.

The obtained values \u200b\u200bof the average hydrogen concentrations at the edge of the destruction 5-10 times higher than its initial content for Article 20, which could not have no significant effect on the damage to the pipes.

The above results indicate that hydrogen embrittlement turned out to be a decisive factor in the damage to the CTEC boilers of boilers.

An additional study required, which of the factors has decisive influence on this process: a) heat cycling due to destabilization of the normal boiling regime in the zones of increased heat fluxes in the presence of deposits on the evaporative surface, and, as a result, damage to its protective oxide films; b) the presence in the working medium of corrosion-active impurities concentrating in sediments in the evaporation surface; c) the joint action of the factors "A" and "B".

It is especially worth the question of the role of fuel regime. The nature of the curves testifies to the accumulation of hydrogen in some cases near the outer surface of the on-screen pipes. This is possible, first of all, in the presence of a dense layer of sulphides on the specified surface, is largely not permeable to hydrogen, diffusing from the inner surface to the outer surface. The formation of sulphides is due to: high sulfurness of burning fuel; Sketch of torch on the on-screen panels. Another reason for the metal floors in the outer surface is the flow of corrosion processes during metal contact with smoke gases. As the analysis of the external sediments of the pipes of the boilers showed, there was usually the action of both reduced reasons.

The role of the flue mode is also manifested in corrosion of screen pipes under the action of pure water, which is most often observed on high pressure steam generators. Corrosion foci is usually located in the zone of maximum local heat loads and only on a heated surface of the pipe. This phenomenon leads to the formation of round or elliptical recesses with a diameter of more than 1 cm.

Metal overheating occurs most often in the presence of deposits due to the fact that the amount of perceived heat will be almost the same as for a pure pipe and for a pipe containing a puff temperature will be different.

This corrosion in size and intensity is often more significant and dangerous than corrosion of boilers during their work.

When leaving water in systems, depending on its temperature and air access, a wide variety of occurrence of parking corrosion may occur. It should be primarily noted by the extreme undesirability of the presence of water in the pipes of the aggregates when they are in reserve.

If water for one or another remaining reasons remains in the system, then strong parking corrosion in the vapor may be observed and especially in the water space (mainly on the waterline) at a water temperature of 60-70 ° C. Therefore, in practice, the intensity of parking corrosion is quite often observed, despite the same regimens of the system and the quality of the water contained in them; The devices with significant thermal accumulation are subjected to stronger corrosion than devices having the size of the furnace and the surface of heating, since the boiler water is cooled in them faster; Its temperature becomes below 60-70 ° C.

At water temperature above 85-90 ° C (for example, with short-term stops of the apparatus), general corrosion decreases, and the corrosion of the metal of the steam space, in which the increased condensation of vapors is observed, can exceed the metal corrosion of water space. Parking corrosion in steam space in all cases is more uniform than in the water space of the boiler.

The development of parking corrosion strongly contributes to the accumulating on the surfaces of the boiler, the slurry, which usually holds moisture. In this regard, significant corrosion sinks are often found in aggregates and pipes along the lower forming and at their ends, i.e., on the areas of the greatest cluster of the sludge.

Conservation methods of equipment in reserve

For the preservation of equipment, the following methods can be applied:

a) drying - removal from water and moisture aggregates;

b) filling them with solutions of caustic soda, phosphate, silicate, sodium nitrite, hydrazine;

c) Filling the technological system with nitrogen.

The method of preservation should be chosen depending on the nature and duration of downtime, as well as from the type and design features of the equipment.

Easy equipment for duration can be divided into two groups: short-term - no more than 3 days and long-term - more than 3 days.

Two types of short downtime are distinguished:

a) scheduled associated with the output to the reserve for weekends due to a drop in the load or withdrawal to the reserve for the night;

b) Forced - due to the failure of pipes or damage to other equipment nodes, to eliminate which no longer stop is required.

Depending on the purpose, long-term downtime can be divided into the following groups: a) the equipment output to the reserve; b) current repairs; c) capital repairs.

With short-term downtime, it is necessary to use conservation by filling with deaerated water with maintaining excess pressure or gas (nitric) method. If emergency stop is needed, then the only acceptable method is a nitrogen conservation.

When the system is derived to the reserve or a long-term simple, without performing repair work, conservation is advisable to be carried out by filling in nitrite or sodium silicate. In these cases, it is possible to use nitrogen conservation, be sure to take measures to create a density of the system in order to prevent excessive gas flow and non-productive operation of nitrogen installation, as well as creating safe conditions for maintaining equipment.

Conservation methods by creating overpressure, filling with nitrogen can be used independently of the structural features of the surface heating surfaces.

To prevent the parking corrosion of the metal during the capital and current repairs, only conservation methods are applicable to create a protective film on the metal surface, which preserves properties for at least 1-2 months after draining the preservative solution, since the emptying and depressurization of the system is inevitable. The validity of the protective film on the surface of the metal after it is processed by its sodium nitrite can reach 3 months.

Methods of preservation using water and solutions of reagents are almost unacceptable to protect against parking corrosion of intermediate boiler steamers due to difficulties associated with filling and subsequent wash.

Methods for the preservation of water-heating and steam boilers of low pressure, as well as other equipment of closed technological contours of heat and water supply in many ways differ from the currently used prevention of parking corrosion to the TPP. Below are the main ways of preventing corrosion in the mode of idle equipment of devices of such circulation systems, taking into account the specifics of their work.

Simplified conservation methods

These methods are advisable to apply for small boilers. They consist in full removal of water from boilers and placing moisture-absorbers: calcined calcium chloride, oversized lime, silica gel at the rate of 1-2 kg per 1 m 3 volume.

This method of preservation is suitable at room temperatures below and above zero. In the premises heated in winter, one of the contact methods of conservation can be implemented. It reduces to filling the entire inner volume of an alkaline solution unit (NaOH, Na 3 P0 4, etc.), which ensures the complete stability of the protective film on the metal surface, even when the fluid is saturated with oxygen.

Typically, solutions containing from 1.5- 2 to 10 kg / m 3 NaOH or 5-20 kg / m 3 Na 3 P0 4, depending on the neutral salts in the original water, are used. Smaller values \u200b\u200brelate to condensate, large - to water containing up to 3000 mg / l of neutral salts.

Corrosion can also be prevented by a method of overpressure in which the steam pressure in the stopped unit is constantly maintained at the level of atmospheric pressure, and the water temperature remains above 100 ° C, which prevents the access of the main corrosion agent - oxygen.

An important condition for the effectiveness and efficiency of any method of protection is the maximum possible tightness of the vapor-water reinforcement to avoid too rapid pressure reduction, losses of a protective solution (or gas) or moisture. In addition, in many cases a preliminary cleaning of surfaces from various sediments (salts, sludge, scale) is useful.

When carrying out various ways to protect against parking corrosion, it is necessary to keep in mind the following.

1. With all types of preservation, pre-removal (flushing) of sedimentary sediments (see above) is necessary to avoid gaining parking corrosion in separate areas of the protected aggregate. Mandatory is the implementation of this event in contact conservation, otherwise intensive local corrosion is possible.

2. For similar reasons, it is desirable to remove in front of the long-term conservation of all types of insoluble deposits (sludge, scale, iron oxides).

3. When unreliable fittings, it is necessary to disable backup equipment from working units using plugs.

Separation of steam and water is less dangerous at contact preservation, but unacceptable with dry and gas protection methods.

The choice of moisture absorbs is determined by the comparative availability of the reagent and the desirability of obtaining the maximum possible specific moisture intensity. The best moisture maker is a grain chloride of calcium. Negative lime is much worse than calcium chloride not only due to less moisture intensity, but also the rapid loss of its activity. Lime absorbs not only moisture from the air, but also carbon dioxide, as a result of which it is covered with a layer of carbon dioxide, which prevents the further absorption of moisture.

The conditions in which elements of steam boilers are located are extremely diverse.

As shown numerous corrosion tests and industrial observations, low-alloyed and even austenitic steel during the operation of boilers can be subjected to intensive corrosion.

The corrosion of the metal surfaces of the steam boilers causes its premature wear, and sometimes leads to serious malfunctions and accidents.

Most emergency stops of boilers fall on through corrosion damage to screen, economy - grain, steam heating pipes and borants of boilers. The appearance of even one corrosion fistula in the direct-flow boiler leads to the stop of the entire block, which is associated with the non-performance of electricity. Corrosion of high and ultra-high drum boilers has become the main cause of failures in the work of the CHP. 90% of failures in work due to corrosion damage occurred on drum boilers with a pressure of 15.5 MPa. A significant amount of corrosion damage to the screen pipes of salt compartments was in the "zones of maximum thermal loads.

Conducted by US specialists by surveys 238 boilers (blocks with a capacity of 50 to 600 MW), 1719 unscheduled downtime were recorded. About 2/3 downtime boilers were caused by corrosion, of which 20% accounted for corrosion of steam generating pipes. In the US, internal corrosion "in 1955 was recognized as a serious problem after commissioning a large number of drum boilers with a pressure of 12.5-17 MPa.

By the end of 1970, about 20% of 610 such boilers were amazed by corrosion. Mainly internal corrosion exposed on-screen pipes, and steamers and economizers were stronger than it. With the improvement of nutrient water quality and the transition to the coordinated phosphating mode, with an increase in the parameters on the drum boilers of US power stations instead of viscous, plastic corrosion damage occurred sudden fragile destruction of the on-screen pipes. "As of J970 tons. For Kotlree with a pressure of 12.5; 14.8 and 17 MPa, the destruction of pipes due to corrosion damage was 30, 33 and 65%, respectively.

In terms of the conditions of the corrosion process, the atmospheric corrosion flows under the action of atmospheric, as well as humid gases; Gas, due to the interaction of metal with various gases - oxygen, chlorine, etc. - at high temperatures, and corrosion in electrolytes, in most cases occurring in aqueous solutions.

By the nature of corrosion processes, the boiler metal may be subject to chemical and electrochemical corrosion, as well as their joint impact.

When the surfaces of the heating of steam boilers occurs, high-temperature gas corrosion in the oxidative and reducing atmospheres of flue gases and low-temperature electrochemical corrosion of the tail surfaces of heating.

Studies found that high-temperature corrosion of heating surfaces is most intensively proceeds only if there are excess free oxygen in the furnace gas and in the presence of molten vanadium oxides.

High-temperature gas or sulphide corrosion in the oxidative atmosphere of flue gases affects the tubes of shirm and convective superheater, the first rows of boiling beams, the metal of distortioning spacers between pipes, racks and suspension.

High-temperature gas corrosion in restoration of the atmosphere was observed on the on-screen pipes of the heat chambers of a series of high and supercritical pressure boilers.

Corrosion of pipes for heating surfaces with a gas side represents a complex physico-chemical process of interaction of flue gases and external sediments with oxides - films and metal pipes. The development of this process is influenced by time-changing intensive heat flows and high mechanical stresses arising from internal pressure and self-compensation.

On the boilers of medium and low pressure "the temperature of the walls of the screens determined by the boiling point of water is lower, and therefore this type of metal destruction is not observed.

Corrosion of heating surfaces from flue gases (outer corrosion) is the process of the destruction of the metal as a result of interaction with combustion products, aggressive gases, solutions and melts of mineral compounds.

Under corrosion of metal understands the gradual destruction of the metal, which is due to the chemical or electrochemical effects of the external environment.

\\ Metal destruction processes resulting from their direct chemical interaction with the environment are chemical corrosion.

Chemical corrosion occurs when the metal with superheated ferry and dry gases. Chemical corrosion in dry gases is called gas corrosion.

In the firebox and gas strokes of the boiler, gas corrosion of the outer surface of the pipes and steaks of steam-heater occurs under the influence of oxygen, carbon dioxide, water vapor, sulfur and other gases; The inner surface of the pipes - as a result of interaction with steam or water.

Electrochemical corrosion in contrast to the chemical is characterized by the fact that the reaction occurring with it is accompanied by the occurrence of electric current.

The carriers of electricity in solutions are the ions present in them due to the dissociation of molecules, and in metals - free electrons:

The intracerene surface is mainly susceptible to electrochemical corrosion. According to modern ideas, its manifestation is due to two independent processes: an anode, in which the metal ions are transferred to the solution in the form of hydrated ions, and cathodic, in which the assimilation of excess electrons depolarizers occurs. Depolarizers may be atoms, ions, molecules that are restored.

According to external signs, the solid (general) and local (local) form of corrosion destruction is distinguished.

With a general corrosion, the entire spoofing surface of heating with an aggressive medium is subjected to corrosion, evenly drowned with the inner or outdoor side. With local corrosion, the destruction occurs in separate areas of the surface, the remaining surface of the metal is not affected by damage.

Local local local stains include corrosive, ulcerative, point, intercrystalline, corrosion cracking, corrosion metal fatigue.

A typical example of destruction from electrochemical corrosion.

Destruction from the outer surface of the HDC 042x5 mm pipes from steel 12x1mf TPP-110 boilers occurred on a horizontal section at the bottom of the lifting-hydraulic loop in the zone adjacent to the sub-screen screen. On the back of the pipe there was a disclosure with a small refinement of the edges at the destroyer. The cause of the destruction was the thinning of the pipe wall of about 2 mm in corrosion due to the weasure of the jet of water. After the stop of the boiler, the 850 t / h with the anthracite binary dust (liquid slag), 25.5 MPa and the temperature of the superheated steam 540 ° C on the pipes remained wet slag and ash in which electrochemical corrosion was intensively flowed. Outside the pipe was covered with a thick layer of buoy hydroxide of iron. The internal diameter of the pipes was within tolerances on the pipes of high and ultra-high pressure boilers. The dimensions of the outer diameter have deviations that go beyond the minus tolerance: the minimum outer diameter. was 39 mm with minimally permissible 41.7 mm. The wall thickness near the damage from corrosion was only 3.1 mm at a nominal pipe thickness of 5 mm.

Metal microstructure is homogeneous in length and circle. On the inner surface of the pipe there is a deductible layer formed during the oxidation of the pipe in the process of heat treatment. There is no such layer on the outside.

Surveys of PCC pipes after the first break made it possible to find out the cause of destruction. It was decided to replace the HPC and about changing the technology of divisions. In this case, electrochemical corrosion proceeded due to the presence of a thin electrolyte film.

Ulcerative corrosion proceeds intensively on certain small areas of the surface, but often to a significant depth. When the diameter of Yazvin is about 0.2-1 mm, it is called point.

In places where yazvins are formed, swearing can be formed. Yazvins are often filled with corrosion products, as a result of which they are not always able to detect them. An example is the destruction of the steel economyzer pipes with poor deaeration of nutritious water and low speeds of water in the pipes.

Despite the fact that a significant part of the pipe metal is amazed, due to through fistulas, it is necessary to completely replace the economizer coils.

The metal of steam boilers is subjected to the following dangerous types of corrosion: oxygen corrosion during the boilers and find them in repair; intercrystallite corrosion in the places of evaporation of boiler water; conducting corrosion; corrosion cracking of elements of boilers made of austenitic steels; After corrosion. The brief characteristic of the specified types of metal corrosion of the boilers is given in Table. Yul.

During the work of boilers, metal corrosion is distinguished by corrosion under load and parking corrosion.

Corrosion under load are most susceptible. Moveless boiler elements in contact with a two-phase medium, i.e., screen and boiling pipes. The inner surface of the economizers and superheater when the boilers are affected by corrosion less. Corrosion under load flows in an enlightening medium.

Parking corrosion is manifested in underestimated. Elements of vertical coins of superheater, conductive pipes of horizontal coins of superheater

Owners of the patent RU 2503747:

Technicia

The invention relates to thermal power and can be used to protect against scale heating pipes of steam and water boilers, heat exchangers, boiler plants, evaporators, heating parts, residential houses and industrial systems in the process of 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 nutrient and, therefore, the boiler water is determined by the presence of impurities that can cause various types of metal corrosion of the inner surfaces of heating, the formation of primary scale on them, as well as a sludge as a source of 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 nutrient water impurities 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 aimed at 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.

The US 1877389 patent proposed a method for removing scale and prevent its formation in hot water 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 processes in 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. A detailed description of 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 applied during various periods of time. The time of the capacity of the potential is determined by the nature and degree of pollution of the metal surface, the composition of the water used, the 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.

An aqueous medium from 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;

It allows you to abandon the processes of softening and deaeration of water, which largely simplifies the technological scheme of boiler rooms and makes it possible to significantly reduce costs during construction and operation.

Possible objects of the method can be water-heating boilers, boilers - utilizers, closed heat supply systems, installation of thermal destruction of seawater, steam mills, and so on.

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, 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 stated method to ensure a non-repetitive, non-valuable mode of operation of the vapor boiler aircraft in the conditions of high-quality water treatment, respect for the water-chemical regime and the high professional level of operation of the 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 at the input to the specified boiler room, as a rule, exceeds the regulatory requirements (0.3 mg / l) and is 0.3-0.5 mg / l, which leads to intensive ingrowth of the inner surfaces by 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. The preliminary inspection of the boiler was produced at the beginning of the 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 until the end of the heating period in order to final purification of drums and boiling pipes and clarify the reliability of providing a non-free operation 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.