RUSSIAN JOINT STOCK COMPANY
ENERGY AND ELECTRIFICATION
"UES of RUSSIA"

DEPARTMENT OF SCIENCE AND TECHNOLOGY

STANDARD INSTRUCTIONS
FOR PERFORMANCE CHEMICAL
CLEANING WATER BOILERS

RD 34.37.402-96

ORGRES

Moscow 1997

DevelopedJSC "Firma ORGRES"

PerformersV.P. SEREBRYAKOV, A.Yu. BULAVKO (JSC Firm ORGRES), S.F. SOLOVIEV(CJSC "Rostenergo"), HELL. Efremov, N.I. SHADRINA(JSC "Kotloochistka")

ApprovedDepartment of Science and Technology of RAO "UES of Russia" 04.01.96

Boss A.P. BERSENEV

Expiry date set

from 01.10.97

INTRODUCTION

1. Typical instruction(hereinafter referred to as the Instruction) is intended for personnel of design, installation, commissioning and operating organizations and is the basis for designing schemes and choosing a technology for cleaning hot water boilers at specific facilities and compiling local work instructions (programs).

2. The instruction was drawn up on the basis of the experience gained in carrying out operational chemical cleaning of hot water boilers last years their operation, and determines general order and conditions for the preparation and conduct of operational chemical cleaning of hot water boilers.

The Instruction takes into account the requirements of the following regulatory and technical documents:

Rules for the technical operation of power plants and networks of the Russian Federation (Moscow: SPO ORGRES, 1996);

Standard instructions for operational chemical cleaning of hot water boilers (M.: SPO Soyuztekhenergo, 1980);

Instructions for analytical control during chemical cleaning of thermal power equipment (Moscow: SPO Soyuztekhenergo, 1982);

Guidelines for water treatment and water chemistry regime of water heating equipment and heating networks: RD 34.37.506-88 (M.: Rotaprint VTI, 1988);

Consumption rates of reagents for pre-start and operational chemical cleaning of thermal power equipment of power plants:HP 34-70-068-83(M.: SPO Soyuztekhenergo, 1985);

Guidelines for the use of calcium hydroxide for the preservation of heat and power and other industrial equipment at the facilities of the USSR Ministry of Energy (Moscow: SPO Soyuztekhenergo, 1989).

3. When preparing and carrying out chemical cleaning of boilers, the requirements of the documentation of the equipment manufacturers involved in the cleaning scheme should also be observed.

4. With release of this Instruction the “Standard instruction for operational chemical cleaning of hot water boilers” (M .: SPO Soyuztekhenergo, 1980) is no longer valid.

1. GENERAL PROVISIONS

1.1. During the operation of hot water boilers, deposits form on the internal surfaces of the water path. Subject to the regulated water regime, the deposits consist mainly of iron oxides. In case of violations of the water regime and the use of low-quality water or blowdown water from power boilers for feeding networks, sediments may also contain (in an amount from 5% to 20%) hardness salts (carbonates), silicon compounds, copper, phosphates.

Subject to the water and combustion regimes, the deposits are evenly distributed along the perimeter and height of the screen pipes. A slight increase in them can be observed in the area of ​​the burners, and a decrease in the area of ​​the hearth. With a uniform distribution of heat fluxes, the amount of deposits on the individual pipes of the screens is basically about the same. On pipes of convective surfaces, deposits are also generally evenly distributed along the perimeter of the pipes, and their amount, as a rule, is less than on pipes of screens. However, in contrast to screened convective surfaces on individual pipes, the difference in the amount of deposits can be significant.

1.2. Determination of the amount of deposits formed on the heating surfaces during the operation of the boiler is carried out after each heating season. To do this, pipe samples with a length of at least 0.5 m are cut out from various sections of the heating surfaces. The number of these samples should be sufficient (but not less than 5 - 6 pieces) to assess the actual contamination of the heating surfaces. AT without fail samples are cut out from screen tubes in the area of ​​burners, from top row the upper convective package and the bottom row of the lower convective package. The need to cut an additional number of samples is specified in each individual case, depending on the operating conditions of the boiler. Determination of the specific amount of deposits (g / m 2) can be performed in three ways: by weight loss of the sample after etching it in an inhibited acid solution, by weight loss after cathodic etching, and by weighing the deposits removed mechanically. The most accurate of these methods is cathodic etching.

The chemical composition is determined from an average sample of deposits removed from the surface of the sample mechanically, or from a solution after etching of the samples.

1.3. Operational chemical cleaning is designed to remove deposits from the inner surface of pipes. It should be carried out when the heating surfaces of the boiler are contaminated with 800 - 1000 g / m 2 or more, or with an increase in the hydraulic resistance of the boiler by 1.5 times compared to the hydraulic resistance of a clean boiler.

The decision on the need for chemical cleaning is made by a commission chaired by the chief engineer of the power plant (head of the heating boiler house) based on the results of analyzes for the specific contamination of heating surfaces, determining the condition of the pipe metal, taking into account the boiler operation data.

Chemical cleaning is usually carried out in summer period when the heating season is over. In exceptional cases, it can be carried out in winter, if the safe operation of the boiler is disturbed.

1.4. Chemical cleaning must be carried out using a special installation, including equipment and pipelines that ensure the preparation of flushing and passivating solutions, their pumping through the boiler path, as well as the collection and disposal of waste solutions. Such an installation must be carried out in accordance with the project and linked to the general plant equipment and schemes for the neutralization and neutralization of waste solutions of the power plant.

2. REQUIREMENTS FOR TECHNOLOGY AND CLEANING SCHEME

2.1. Washing solutions should provide high-quality cleaning surfaces, taking into account the composition and amount of deposits present in the boiler screen pipes and to be removed.

2.2. It is necessary to assess the corrosion damage to the pipe metal of the heating surfaces and select the conditions for cleaning with a cleaning solution with the addition of effective inhibitors to reduce pipe metal corrosion during cleaning to acceptable values ​​and limit the appearance of leaks during chemical cleaning of the boiler.

2.3. The cleaning scheme should ensure the efficiency of cleaning the heating surfaces, the completeness of the removal of solutions, sludge and suspension from the boiler. Cleaning of boilers according to the circulation scheme should be carried out with the speeds of movement of the washing solution and water, providing the specified conditions. In this case, the design features of the boiler, the location of convective packs in the boiler water path and the presence of a large number of horizontal pipes small diameter with multiple bends of 90 and 180°.

2.4. It is necessary to carry out neutralization of residual acid solutions and post-flushing passivation of the heating surfaces of the boiler to protect against corrosion when the boiler is idle for 15 to 30 days or subsequent conservation of the boiler.

2.5. At the choice of technology and treatment scheme should take into account environmental requirements and provide for installations and equipment for the neutralization and disposal of waste solutions.

2.6. All technological operations should be carried out, as a rule, when washing solutions are pumped through the water path of the boiler along a closed circuit. The speed of movement of cleaning solutions during cleaning of hot water boilers should be at least 0.1 m/s, which is acceptable, as it ensures uniform distribution of the cleaning agent in the pipes of the heating surfaces and a constant supply of fresh solution to the surface of the pipes. Water washes must be carried out for discharge at speeds of at least 1.0 - 1.5 m/s.

2.7. Waste cleaning solutions and the first portions of water during water washing should be sent to the plant-wide neutralization and neutralization unit. Water is drained into these installations until a pH value of 6.5 - 8.5 is reached at the outlet of the boiler.

2.8. When performing all technological operations (with the exception of the final water washing with network water according to the standard scheme), process water is used. It is permissible to use network water for all operations, if possible.

3. CHOICE OF CLEANING TECHNOLOGY

3.1. For all types of deposits found in hot water boilers, hydrochloric or sulfuric acid, sulfuric acid with ammonium hydrofluoride, sulfamic acid, low molecular weight acid concentrate (NMA) can be used as a washing agent.

The choice of cleaning solution is made depending on the degree of contamination of the boiler heating surfaces to be cleaned, the nature and composition of deposits. To develop a technological regime for cleaning, samples of pipes cut out from the boiler with deposits are processed in laboratory conditions with the selected solution while maintaining the optimal performance of the cleaning solution.

3.2. Hydrochloric acid is mainly used as a detergent. This is due to its high detergent properties, which allow cleaning of any type of deposits from heating surfaces, even with high specific contamination, as well as the lack of a reagent.

Depending on the amount of deposits, cleaning is carried out in one (with contamination up to 1500 g / m 2) or in two stages (with greater contamination) with a solution with a concentration of 4 to 7%.

3.3. Sulfuric acid is used to clean heating surfaces from iron oxide deposits with a calcium content of not more than 10%. In this case, the concentration of sulfuric acid, according to the conditions for ensuring its reliable inhibition during the circulation of the solution in the purification circuit, should be no more than 5%. When the amount of deposits is less than 1000 g/m 2, one stage of acid treatment is sufficient, with contamination up to 1500 g/m 2, two stages are required.

When only vertical pipes (screen heating surfaces) are cleaned, it is acceptable to use the etching method (without circulation) with a solution of sulfuric acid with a concentration of up to 10%. With the amount of deposits up to 1000 g/m 2 one acid stage is required, with more contamination - two stages.

As a washing solution for removing iron oxide (in which calcium is less than 10%) deposits in an amount of not more than 800 - 1000 g / m 2, a mixture of a dilute solution of sulfuric acid (concentration less than 2%) with ammonium hydrofluoride (of the same concentration) can also be recommended. the mixture is characterized by an increased rate of dissolution of deposits compared to sulfuric acid. A feature of this purification method is the need to periodically add sulfuric acid to maintain the pH of the solution at an optimal level of 3.0 - 3.5 and to prevent the formation of Fe hydroxide compounds ( III).

The disadvantages of methods using sulfuric acid include the formation of a large amount of suspension in the cleaning solution during the cleaning process and a lower rate of dissolution of deposits compared to hydrochloric acid.

3.4. If the heating surfaces are contaminated with deposits of carbonate-iron oxide composition in an amount up to 1000 g/m 2, sulfamic acid or NMA concentrate can be used in two stages.

3.5. When using all acids, it is necessary to add corrosion inhibitors to the solution, which protect the boiler metal from corrosion under the conditions of use of this acid (acid concentration, solution temperature, presence of washing solution movement).

For chemical cleaning, as a rule, inhibited hydrochloric acid is used, into which one of the corrosion inhibitors PB-5, KI-1, B -1 (B-2). When preparing a washing solution of this acid, an inhibitor of urotropin or KI-1 must be additionally introduced.

For solutions of sulfuric and sulfamic acids, ammonium hydrofluoride, MNK concentrate, mixtures of catapine or catamine AB with thiourea or thiuram or captax are used.

3.6. If the contamination is above 1500 g/m 2 or if there is more than 10% silicic acid or sulfates in the deposits, it is recommended to perform alkaline treatment before acid treatment or between acid stages. Alkalinization is usually carried out between the acid stages with a solution of caustic soda or a mixture of it with soda ash. Adding 1-2% soda ash to caustic soda increases the effect of loosening and removing sulfate deposits.

In the presence of deposits in the amount of 3000 - 4000 g/m 2 cleaning of heating surfaces may require successive alternation of several acidic and alkaline treatments.

To intensify the removal of solid iron oxide deposits, which are located in the lower layer, and if there are more than 8–10% silicon compounds in the deposits, it is advisable to add fluorine-containing reagents (fluoride, ammonium or sodium hydrofluoride) to the acid solution, added to the acid solution after 3–4 hours after the start of processing.

In all these cases, preference should be given to hydrochloric acid.

3.7. For post-flush passivation of the boiler, in cases where it is necessary, one of the following treatments is used:

a) treatment of the cleaned heating surfaces with 0.3 - 0.5% sodium silicate solution at a solution temperature of 50 - 60 ° C for 3 - 4 hours with the circulation of the solution, which will provide protection against corrosion of the boiler surfaces after draining the solution in wet conditions in for 20 - 25 days and in a dry atmosphere for 30 - 40 days;

b) treatment with a solution of calcium hydroxide in accordance with the guidelines for its use for the conservation of boilers.

4. CLEANING SCHEMES

4.1. The scheme of chemical cleaning of a hot water boiler includes the following elements:

boiler to be cleaned;

a tank designed for the preparation of cleaning solutions and serving at the same time as an intermediate container when organizing the circulation of cleaning solutions in a closed circuit;

flushing pump for mixing solutions in the tank through the recirculation line, supplying the solution to the boiler and maintaining the required flow rate when pumping the solution along a closed circuit, as well as for pumping the spent solution from the tank to the neutralization and neutralization unit;

pipelines that combine the tank, pump, boiler into a single cleaning circuit and ensure the pumping of the solution (water) through closed and open circuits;

neutralization and neutralization unit, where waste cleaning solutions and contaminated water are collected for neutralization and subsequent neutralization;

hydroash removal channels (GZU) or industrial storm sewerage (PLC), where conditionally clear waters(with pH 6.5 - 8.5) when washing the boiler from suspended solids;

tanks for storing liquid reagents (primarily hydrochloric or sulfuric acid) with pumps for supplying these reagents to the purification circuit.

4.2. The rinsing tank is intended for preparation and heating of washing solutions, it is a blending tank and a place for gas outlet from the solution in the circulation circuit during cleaning. The tank must have an anti-corrosion coating, must be equipped with a loading hatch with a grid with a mesh size of 10´ 10 ÷ 15 ´ 15 mm or perforated bottom with holes of the same size, level glass, thermometer sleeve, overflow and drain pipes. The tank must have a fence, a ladder, a device for lifting bulk reagents, and lighting. Pipelines for supplying liquid reagents, steam, water must be connected to the tank. Solutions are heated with steam through a bubbling device located at the bottom of the tank. It is advisable to bring hot water from the heating network (from the return line) into the tank. Process water can be supplied both to the tank and to the suction manifold of the pumps.

The capacity of the tank must be at least 1/3 of the volume of the flush circuit. When determining this value, it is necessary to take into account the capacity of the network water pipelines included in the cleaning circuit, or those that will be filled during this operation. As practice shows, for boilers with a thermal capacity of 100 - 180 Gcal / h, the volume of the tank must be at least 40 - 60 m 3.

For uniform distribution and facilitating the dissolution of bulk reagents, it is advisable to lead a pipeline with a diameter of 50 mm with a rubber hose from the recirculation pipeline into the tank for mixing solutions into the loading hatch.

4.3. The pump intended for pumping the washing solution along the cleaning circuit must provide a speed of at least 0.1 m / s in the pipes of the heating surfaces. The choice of this pump is made according to the formula

Q= (0.15 ÷ 0.2) S 3600,

where Q- pump flow, m 3 / h;

0.15 ÷ 0.2 - the minimum speed of the solution, m/s;

S- area of ​​maximum cross section boiler water path, m 2;

3600 - conversion factor.

For chemical cleaning of hot water boilers with a thermal output of up to 100 Gcal / h, pumps with a flow rate of 350 - 400 m 3 / h can be used, and for cleaning boilers with a thermal output of 180 Gcal / h - 600 - 700 m 3 / h. The pressure of the flushing pumps must not be less than the hydraulic resistance of the flushing circuit at a speed of 0.15 - 0.2 m/s. This speed for most boilers corresponds to a head of no more than 60 m of water. Art. For pumping cleaning solutions, two pumps are installed for pumping acids and alkalis.

4.4. The pipelines intended for organizing the pumping of cleaning solutions in a closed circuit must have diameters not less than the diameters of the suction and pressure nozzles of the washing pumps, respectively, the pipelines for draining waste washing solutions from the cleaning circuit to the neutralization tank may have diameters that are significantly smaller than the diameters of the main pressure-return ( waste) collectors.

The cleaning circuit must provide for the possibility of draining all or most of the cleaning solution into the tank.

The diameter of the pipeline intended for the removal of wash water into the industrial storm channel or the GZU system must take into account the throughput of these lines. The pipelines of the boiler cleaning circuit must be stationary. Their routing must be chosen in such a way that they do not interfere with the maintenance of the main equipment of the boiler during operation. The fittings on these pipelines should be located in accessible places, the routing of the pipelines should ensure their emptying. If there are several boilers at the power plant (heating boiler house), common pressure-return (discharge) collectors are installed, to which pipelines are connected, designed to clean a separate boiler. Shut-off valves must be installed on these pipelines.

4.5. The collection of washing solutions coming from the tank (along the overflow line, drainage line), from the sampler troughs, from pump leaks through stuffing boxes, etc., should be carried out in a pit, from where they are sent to the neutralization unit by a special pumping pump.

4.6. When carrying out acid treatments, fistulas are often formed in the heating surfaces of the boiler and pipelines of the flushing scheme. Violation of the density of the cleaning circuit can occur at the beginning of the acid stage, and the amount of washing solution loss will not allow further operation. To speed up the emptying of the defective section of the heating surface of the boiler and the subsequent safe repair work to eliminate the leak, it is advisable to upper part boiler to supply nitrogen or compressed air. For most boilers, the boiler vents are a convenient connection point.

4.7. The direction of movement of the acid solution in the boiler circuit must take into account the location of the convective surfaces. It is advisable to organize the direction of solution movement in these surfaces from top to bottom, which will facilitate the removal of exfoliated sediment particles from these elements of the boiler.

4.8. The direction of movement of the washing solution in the screen pipes can be any, since with an upward flow at a speed of 0.1 - 0.3 m / s, the smallest suspended particles will pass into the solution, which at these speeds will not be deposited in the coils of convective surfaces when moving from above down. Large sediment particles, for which the movement speed is less than the soaring speed, will accumulate in the lower collectors of the screen panels, therefore, their removal from there must be carried out by intensive water washing at a water speed of at least 1 m/s.

For boilers with convective surfaces are the outlet sections of the water path, it is advisable to organize the flow direction so that they are the first in the direction of the washing solution when pumping along a closed circuit.

The cleaning circuit must be able to change the flow direction to the opposite, for which a jumper must be provided between the pressure and discharge pipelines.

Ensuring the rate of movement of wash water above 1 m/s can be achieved by connecting the boiler to the heating main, while the scheme should provide for pumping water along a closed circuit with a constant removal of wash water from the boiler circuit while simultaneously supplying water to it. The amount of water supplied to the purification circuit must correspond to bandwidth waste channel.

In order to constantly remove gases from individual sections of the water path, the boiler air vents are combined and discharged into the flushing tank.

The connection of the pressure-return (discharge) pipelines to the water path should be made as close as possible to the boiler. To clean the sections of the network water pipeline between the sectional valve and the boiler, it is advisable to use the bypass line of this valve. In this case, the pressure in the water path must be less than in the network water pipeline. In some cases, this line can serve as an additional source of water entering the purification circuit.

4.9. To increase the reliability of the cleaning circuit and greater safety during its maintenance, it must be equipped with steel reinforcement. In order to exclude the overflow of solutions (water) from the pressure pipeline to the return pipeline through the jumper between them, to pass them into the discharge channel or the neutralization tank and to be able to install, if necessary, a plug, the fittings on these pipelines, as well as on the recirculation line to the tank, must be flanged. The principal (general) scheme of the plant for chemical cleaning of boilers is shown in fig. .

4.10. During chemical cleaning of PTVM-30 and PTVM-50 boilers (Fig. ,), the flow area of ​​the water path when using pumps with a feed rate of 350 - 400 m 3 / h provides a solution movement speed of about 0.3 m / s. The sequence of passage of the washing solution through the heating surfaces may coincide with the movement of network water.

When cleaning the boiler PTVM-30 Special attention it is necessary to pay attention to the organization of the removal of gases from the upper collectors of the screen panels, since the direction of the solution movement has multiple changes.

For the PTVM-50 boiler, it is advisable to supply the cleaning solution to the direct network water pipeline, which will allow organizing the direction of its movement in the convective package from top to bottom.

4.11. During chemical cleaning of the KVGM-100 boiler (Fig. ), the pipelines for supplying and returning cleaning solutions are connected to the pipelines of return and direct network water. The movement of the medium is carried out in the following sequence: front screen - two side screens - intermediate screen - two convective beams - two side screens - rear screen. When passing through the water path, the washing flow repeatedly changes the direction of the medium. Therefore, when cleaning this boiler, special attention should be paid to the organization of a constant removal of gases from the upper screen surfaces.

4.12. During the chemical cleaning of the PTVM-100 boiler (Fig. ), the movement of the medium is organized either according to a two- or four-way scheme. When using a two-way scheme, the speed of the medium will be about 0.1 - 0.15 m/s when using pumps with a flow of about 250 m 3 / h. When organizing a two-way movement scheme, the pipelines for supplying and discharging the washing solution are connected to the pipelines of the return and direct network water.

When using a four-way scheme, the speed of the movement of the medium when using pumps of the same supply is doubled. The connection of the pipelines for supplying and discharging the washing solution is organized into bypass pipelines from the front and rear screens. The organization of a four-way scheme requires the installation of a plug on one of these pipelines.

Rice. 1. Scheme of installation for chemical cleaning of the boiler:

1 - flushing tank; 2 - flushing pumps ;

Rice. 2. Scheme of chemical cleaning of the boiler PTVM-30:

1 - rear additional screens; 2 - convective beam; 3 - side screen of the convective shaft; 4 - side screen; 5 - front screens; 6 - rear screens;

Valve closed

Rice. 3. Scheme of chemical cleaning of the boiler PTVM-50 :

1 - right side screen; 2 - upper convective beam; 3 - lower convective beam; 4 - rear screen; 5 - left side screen; 6 - front screen;

Valve closed

Rice. 4. Scheme of chemical cleaning of the boiler KVGM-100 (main mode):

1 - front screen; 2 - side screens; 3 - intermediate screen; 4 - side screen; 5 - rear screen; 6 - convective beams;

Valve closed

Rice. 5. Scheme of chemical cleaning of the boiler PTVM-100:

a - two-way; b - four-way;

1 - left side screen; 2 - rear screen; 3 - convective beam; 4 - right side screen; 5 - front screen;

The movement of the medium when using a two-way scheme corresponds to the direction of movement of water in the water path of the boiler during its operation. When using a four-way scheme, the passage of the heating surfaces with a washing solution is carried out in the following sequence: front screen - convective packages of the front screen - side (front) screens - side (rear) screens - convective packages of the rear screen - rear screen.

The direction of movement can be reversed when changing the purpose of the temporary pipes connected to the boiler bypass pipes.

4.13. During chemical cleaning of the PTVM-180 boiler (Fig. , ), the movement of the medium is organized either according to a two- or four-way scheme. When organizing the pumping of the medium according to a two-way scheme (see Fig. ), the pressure-discharge pipelines are connected to the pipelines of the return and direct network water. With such a scheme, it is preferable to direct the medium in convective packets from top to bottom. To create a movement speed of 0.1 - 0.15 m/s, it is necessary to use a pump with a feed rate of 450 m 3 / h.

When pumping the medium according to a four-way scheme, the use of a pump of such a supply will provide a speed of 0.2 - 0.3 m / s.

The organization of a four-way scheme requires the installation of four plugs on the bypass pipelines from the distributing upper network water collector to the double-light and side screens, as shown in fig. . The connection of pressure and discharge pipelines in this scheme is carried out to the return network water pipeline and to all four bypass pipes, plugged from the return network water chamber. Given that the bypass pipes haveD at 250 mm and for most of its routing - turning sections, connecting pipelines to organize a four-way scheme requires a lot of labor.

When using a four-way scheme, the direction of movement of the medium along the heating surfaces is as follows: the right half of the two-light and side screens - the right half of the convective part - the back screen - the direct network water chamber - the front screen - the left half of the convective part - the left half of the side and two-light screens.

Rice. 6. Scheme of chemical cleaning of the boiler PTVM-180 (two-way scheme):

1 - rear screen; 2 - convective beam; 3 - side screen; 4 - two-light screen; 5 - front screen;

Valve closed

Rice. 7. Scheme of chemical cleaning of the boiler PTVM-180 (four-way scheme):

1 - rear screen; 2- convective beam; 3- side screen; 4 - two-light screen; 5 - front screen ;

4.14. During chemical cleaning of the KVGM-180 boiler (Fig. ), the movement of the medium is organized according to a two-way scheme. The speed of movement of the medium in the heating surfaces at a flow rate of about 500 m 3 /h will be about 0.15 m/s. Pressure-return pipelines are connected to pipelines (chambers) of return and direct network water.

The creation of a four-pass scheme for the movement of the medium in relation to this boiler requires significantly more alterations than for the PTVM-180 boiler, and therefore its use when performing chemical cleaning is impractical.

Rice. 8. Scheme of chemical cleaning of the KVGM-180 boiler:

1 - convective beam; 2 - rear screen; 3- ceiling screen; 4 - intermediate screen; 5 - front screen;

Valve closed

The direction of movement of the medium in the heating surfaces should be organized taking into account the change in the direction of the flow. In acidic and alkaline treatments, it is advisable to direct the movement of the solution in convective packages from the bottom up, since these surfaces will be the first in the circulation loop along a closed loop. When washing with water, it is advisable to periodically reverse the flow movement in convective packs.

4.15. Washing solutions are prepared either in portions in a washing tank with their subsequent pumping into the boiler, or by adding a reagent to the tank while circulating heated water through a closed cleaning circuit. The amount of the prepared solution must correspond to the volume of the cleaning circuit. The amount of solution in the circuit after the organization of pumping in a closed circuit should be minimal and determined necessary level for reliable operation pump, which is ensured by maintaining a minimum level in the tank. This allows you to add acid during processing to maintain the desired concentration or pH. Each of the two methods is acceptable for all acidic solutions. However, when performing purification using a mixture of ammonium hydrofluoride with sulfuric acid, the second method is preferred. The dosage of sulfuric acid in the cleaning circuit is best done in the upper part of the tank. Acid injection can be done either plunger pump supply of 500 - 1000 l / h, or by gravity from a tank installed at a mark above the flushing tank. Corrosion inhibitors for cleaning solution based on hydrochloric or sulfuric acid do not require special dissolution conditions. They are loaded into the tank before acid is introduced into it.

A mixture of corrosion inhibitors used for cleaning solutions of sulfuric and sulfamic acids, a mixture of ammonium hydrofluoride with sulfuric acid and NMA, is prepared in a separate container in small portions and poured into the tank hatch. The installation of a special tank for this purpose is not necessary, since the amount of the prepared mixture of inhibitors is small.

5. TECHNOLOGICAL MODES OF CLEANING

Approximate technological regimes used to clean boilers from various deposits, in accordance with Sec. are given in table. .

Table 1