Experience in preservation of hot water boilers with sodium silicate. Conservation of power-generating steam boilers. Brief information about air drying and heating plants
СО - the first stage, further conservation depends on the subsequent period of repair, reserve
Notes:
1. On boilers with a pressure of 9.8 and 13.8 MPa without treatment of feed water with hydrazine, it is recommended to carry out maintenance at least once a year.
2. A - filling the boiler heating surfaces with nitrogen.
3. Hydraulic fracturing + CO - hydrazine treatment at the operating parameters of the boiler, followed by dry shutdown; GO + ZSch, TO + ZSh, FV + ZSch - filling the boiler with an alkaline solution with the previous reagent treatment;
4. TO + CI - conservation with a contact inhibitor with a previous trilon treatment;
5. "Before", "after" - before and after the repair.
5. Methods for preserving hot water boilers
5.1. Preservation with calcium hydroxide solution
5.1.1. The method of preservation with a calcium hydroxide solution is based on the highly effective inhibiting properties of a calcium hydroxide Ca (OH) 2 solution. The protective concentration of calcium hydroxide is 0.7 g / kg and higher.
This method is regulated.
5.1.2. When preserving the heating surfaces of hot water boilers by filling with calcium hydroxide solution, the proposed measures achieve the following effect:
Formation of a stable protective film upon contact with a metal of calcium hydroxide solution within 3 - 4 weeks
Preservation for 2 - 3 months of the protective effect of the films when emptying the boiler from the solution after contact for 3 - 4 weeks or more.
Full filling of the boiler with calcium hydroxide solution during conservation
The possibility of draining the solution for repair work after holding in the boiler for 3 - 4 weeks
Application of the method for the conservation of hot water boilers of any type at power plants with water treatment plants with lime economy.
Conducting preservation with calcium hydroxide solution when putting the boiler into reserve for up to 6 months. or withdrawal for repair for up to 3 months.
5.1.3. Preservation of heating surfaces of hot water boilers filled with calcium hydroxide solution is recommended to be carried out by performing the proposed measures, maintaining the following parameters and maximizing the possibilities of the scheme:
Preparation of calcium hydroxide solution in wet lime storage cells with a floating suction device (Figure 4)
Settling of lime milk for 10 - 12 hours until the solution is completely clarified after filling lime (fluff, construction lime, calcium carbide quenching waste) into the cells and mixing
Preservation of the concentration of calcium hydroxide in a solution of no more than 1.4 g / kg due to its low solubility at a temperature of 10 - 25 ° С
Controlling the position of the floating suction device when pumping out the solution from the cell, preventing the capture of sediments from the bottom of the cell
Possibilities of use for filling boilers with a solution of the acid washing scheme of hot water boilers, shown in Figure 6
Draining water from the boiler before filling it with a preservative solution
By pumping calcium hydroxide solution from lime cells to the tank for preparation of reagents
Flushing the pipeline with water before pumping in order to avoid getting into the tank of milk of lime supplied through this pipeline for preliminary cleaning of the water treatment plant
Filling the boiler when circulating the solution along the contour "tank - pump - solution supply pipeline - boiler - solution discharge pipeline - tank"
Determination of the amount of prepared lime mortar, based on ensuring the filling of the preserved boiler and the circulation pattern, including the tank. When filling the boiler with a pump from the tank without organizing circulation through the boiler, the volume of prepared milk of lime depends only on the water volume of the boiler. The water volume of boilers PTVM-50, PTVM-100, PTVM-180 is 16, 35 and 60 m3, respectively.
Preservation of the preservative solution in the boiler for the entire downtime in reserve, with tight closing of all shut-off valves on the boiler
1 - tank for preparation of chemical reagents;
2 - pump for filling the boiler with a solution of chemical reagents;
3 - make-up water; 4 - chemical reagents;
5 - milk of lime into pretreatment mixers;
6 - cells of lime milk; 7 - hot water boilers;
8 - to other hot water boilers; 9 - from other hot water boilers.
Figure 6 - Scheme of conservation of hot water boilers.
The possibility of draining the solution if it is necessary to carry out repair work after holding in the boiler for at least 3 - 4 weeks with the expectation of turning the boiler into operation after the repair is completed.
Checking the pH value of the solution at least once every two weeks, while maintaining the preservation solution in the boiler for the duration of the downtime
The organization of circulation of the solution through the boiler for the selection of control analyzes
Sampling from air vents during circulation
Draining the solution from the entire circuit, if the pH value is ³ 8.3 and filling with a fresh solution of calcium hydroxide
Carrying out the drainage of the preservative solution from the boiler at a low flow rate, diluting it with water to the pH value< 8,5
By draining and flushing the boiler with network water to the hardness of the flushing water before starting, if the boiler was filled with a preservative solution.
5.2. Preservation with sodium silicate solution
5.2.1. Sodium silicate (liquid sodium glass) forms a strong, dense protective film on the metal surface in the form of Fe3O4 · FeSiO3 compounds. This film shields the metal from corrosive agents (CO2 and O2).
5.2.2. The formation of a protective film occurs when the preservative solution is kept in the boiler for several days or when the solution is circulated through the boiler for several hours.
5.2.3. It is recommended to preserve the heating surfaces of hot water boilers with sodium silicate by maintaining the following concentrations and performing the proposed organizational and technical measures:
Full filling of a hot water boiler with a sodium silicate solution with a SiO2 concentration in a preservative solution of at least 1.5 g / kg
The use of sodium silicate for the preservation of hot water boilers of all types
Conducting conservation with sodium silicate when putting the boiler into reserve for up to 6 months. or for repairs for up to 2 months.
Use for filling boilers with a solution of the acid flushing scheme of hot water boilers, shown in Figure 6
Possibilities of using the existing tank with a pump for the conservation of power boilers (Figure 2)
Preparation of sodium silicate solution in softened water, since the use of water with a hardness higher than 3 mg eq / kg can lead to the precipitation of sodium silicate flakes from the solution
Preparation of a preservative solution of sodium silicate in a tank with water circulation according to the "tank-pump-tank" scheme with pouring liquid glass into the tank through the hatch
Determination of the approximate consumption of liquid commercial sodium silicate at the rate of no more than 6 liters per 1 m3 of the volume of the preservative solution
Draining water from the boiler before filling it with a preservative solution
Establishing the working concentration of SiO2 in the preservative solution at the level of 1.5 - 2 g / kg
Determination of the amount of prepared solution, based on ensuring the filling of the preserved boiler and the circulation pattern, including the tank. When filling the boiler with a pump from the tank without organizing circulation through the boiler, the volume of prepared milk of lime depends only on the water volume of the boiler. When filling the boiler without organizing circulation, the volume of the prepared solution depends only on the volume of the boiler.
Preservation of the preservative solution in the boiler for the entire downtime in reserve
The possibility of draining the solution if it is necessary to carry out repair work after holding in the boiler for at least 4 - 6 days with the expectation of turning the boiler into operation after the completion of the repair.
Drainage of the solution from the boiler for repairs after circulation of the solution through the boiler for 8 - 10 hours at a speed of 0.5 - 1 m / s
Maintaining an overpressure of 0.01 - 0.02 MPa with network water by opening the bypass valve at the boiler inlet while maintaining a preservative solution in it for the entire downtime
Taking a sample from the air vents during the conservation period once a week to control the concentration of SiO2 in the solution
Adding the required amount of liquid sodium silicate and organizing the circulation of the solution through the boiler into the tank until the required concentration is reached with a decrease in the concentration of SiO2 less than 1.5 g / kg
Displacement of the preservative solution into the mains water pipelines in small portions (by partially opening the valve at the boiler outlet) of 5 m3 / h for 5 - 6 hours for the PTVM-100 boiler and 10 - 12 hours for the PTVM-180 boiler when de-preserving the hot water boiler before kindling it.
5. METHODS FOR PRESERVATION OF WATER BOILERS
5.1. Preservation with calcium hydroxide solution
5.1.1. The method is based on highly effective inhibiting properties of calcium hydroxide Ca (OH) solution.
The protective concentration of calcium hydroxide is 0.7 g / kg and higher.
Upon contact with the metal of the calcium hydroxide solution, a stable protective film forms within 3-4 weeks.
When emptying the boiler from the solution after contact for 3-4 weeks or more, the protective effect of the films remains for 2-3 months.
This method is regulated by "Guidelines for the use of calcium hydroxide for the conservation of heat and power and other industrial equipment at the facilities of the Ministry of Energy RD 34.20.593-89" (Moscow: SPO Soyuztekhenergo, 1989).
5.1.2. When implementing this method, the boiler is completely filled with solution. If repair work is required, the solution after holding in the boiler for 3-4 weeks. can be trained.
5.1.3. Calcium hydroxide is used for the preservation of all types of hot water boilers in power plants with lime-based water treatment plants.
5.1.4. Preservation with calcium hydroxide is carried out when the boiler is taken into reserve for a period of up to 6 months or when it is taken out for repairs for a period of up to 3 months.
5.1.5. Calcium hydroxide solution is prepared in wet lime storage cells with a floating suction device (Fig. 4). After the lime (fluff, construction lime, calcium carbide quenching waste) is put into the cells and mixing, the milk of lime is allowed to settle for 10-12 hours until the solution is completely clarified. Due to the low solubility of calcium hydroxide at a temperature of 10-25 ° C, its concentration in the solution will not exceed 1.4 g / kg.
Fig. 4. Scheme of conservation of hot water boilers:
1 - tank for preparation of chemical reagents; 2 - boiler filling pump
a solution of chemical reagents; 3 - make-up water; 4 - chemical reagents;
5 - milk of lime into pretreatment mixers, 6 - cells of milk of lime;
7 - hot water boilers; 8 - to other hot water boilers;
9 - from other hot water boilers;
conservation pipelines
When pumping the solution out of the cell, it is necessary to monitor the position of the floating suction device, not allowing the trapping of deposits on the bottom of the cell.
5.1.6. To fill the boilers with a solution, it is advisable to use the scheme of acid washing of hot water boilers, shown in Fig. 4. A tank with a pump for preserving power boilers can also be used (see Fig. 2).
5.1.7. Before filling the boiler with a preservative solution, water is drained from it.
Calcium hydroxide solution is pumped into the tank for preparation of reagents from lime cells. Before pumping, the pipeline is flushed with water to prevent lime milk from entering the tank supplied through this pipeline to the pre-treatment of the water treatment plant.
It is advisable to fill the boiler when recirculating the solution along the contour "tank-pump-pipeline of solution supply-boiler-pipeline of solution discharge-tank". In this case, the amount of prepared lime mortar must be sufficient to fill the preserved boiler and the recirculation circuit, including the tank.
If the boiler is filled with a pump from the tank without organizing recirculation through the boiler, then the volume of prepared lime milk depends on the water volume of the boiler.
The water volume of boilers PTVM-50, PTVM-100, PTVM-180 is 16, 35 and 60 m3, respectively.
5.1.8. When withdrawing to the reserve, the boiler is left filled with solution for the entire downtime.
5.1.9. If it is necessary to carry out repair work, the drainage of the solution is carried out after holding in the boiler for at least 3-4 weeks in such a way that after the repair is completed, the boiler is put into operation. It is desirable that the duration of the repair does not exceed 3 months.
5.1.10. If the boiler remains with a preservative solution for the period of shutdown, then it is necessary to check the pH value of the solution at least once every two weeks. For this, the solution is recirculated through the boiler, samples are taken from the air vents. If the pH value is 8.3, the solution from the entire circuit is drained and filled with fresh calcium hydroxide solution.
5.1.11. Drainage of the preservative solution from the boiler is carried out at a low flow rate, diluting it with water to a pH value of 5.1.12. Before starting, the boiler is flushed with network water to the hardness of the flushing water, having previously drained it if it was filled with a solution.
5.2. Preservation with sodium silicate solution
5.2.1. Sodium silicate (liquid sodium glass) forms a strong, dense protective film on the metal surface in the form of FeO · FeSiO compounds. This film shields the metal from corrosive agents (CO and O).
5.2.2. When implementing this method, the boiler is completely filled with a sodium silicate solution with a SiO concentration in the preservative solution of at least 1.5 g / kg.
The formation of a protective film occurs when the preservative solution is kept in the boiler for several days or when the solution is circulated through the boiler for several hours.
5.2.3. Sodium silicate is used for the preservation of all types of hot water boilers.
5.2.4. Conservation with sodium silicate is carried out when the boiler is taken into reserve for up to 6 months or when the boiler is taken out for repair for up to 2 months.
5.2.5. To prepare and fill the boiler with sodium silicate solution, it is advisable to use the acid washing scheme for hot water boilers (see Fig. 4). A tank with a pump for preserving power boilers can also be used (see Fig. 2).
5.2.6. A solution of sodium silicate is prepared in softened water, since the use of water with a hardness of more than 3 meq / kg can lead to the precipitation of sodium silicate flakes from the solution.
A preservative solution of sodium silicate is prepared in a tank with water circulation according to the "tank-pump-tank" scheme. Liquid glass is poured into the tank through the hatch.
5.2.7. The approximate consumption of liquid commercial sodium silicate corresponds to no more than 6 liters per 1 m of the volume of the preservative solution.
5.2.8. Before filling the boiler with a preservative solution, water is drained from it.
The working concentration of SiO in the preservative solution should be 1.5-2 g / kg.
It is advisable to fill the boiler when recirculating the solution along the contour "tank-pump-pipeline of solution supply-boiler-pipeline of solution discharge-tank". In this case, the required amount of sodium silicate is calculated taking into account the volume of the entire circuit, including the tank and pipelines, and not only the volume of the boiler.
If the boiler is filled without recirculation, then the volume of the prepared solution depends on the volume of the boiler (see paragraph 5.1.7).
5.2.9. When withdrawing to the reserve, the boiler is left filled with a preservative solution for the entire downtime.
5.2.10. If it is necessary to carry out repair work, the drainage of the solution is carried out after holding in the boiler for at least 4-6 days in such a way that after the repair is completed, the boiler is put into operation.
The solution can be drained from the boiler for repairs after circulation of the solution through the boiler for 8-10 hours at a speed of 0.5-1 m / s.
The duration of the repair should not exceed 2 months.
5.2.11. If the boiler remains with a preservative solution during its downtime, an overpressure of 0.01-0.02 MPa with network water is maintained in it by opening the bypass valve at the boiler inlet. During the conservation period, samples are taken from the air vents once a week to control the concentration of SiO in the solution. When the concentration of SiO decreases to less than 1.5 g / kg, the required amount of liquid sodium silicate is added to the tank and the solution is recirculated through the boiler until the required concentration is reached.
5.2.12. The de-preservation of a hot water boiler is carried out before it is kindled by displacing the preservative solution into the pipelines of the network water in small portions (by partially opening the valve at the outlet of the boiler) 5 m3 / h each for 5-6 hours for the PTVM-100 boiler and 10-12 hours for the PTVM boiler -180.
With open heat supply systems, the preservative solution should be displaced from the boiler without exceeding the MPC standards - 40 mg / kg SiO in the network water.
6. METHODS FOR CONSERVATION OF TURBO UNITS
6.1. Preservation with heated air
6.1.1. Blowing the turbine with hot air prevents moist air from entering the internal cavities and the occurrence of corrosive processes. Particularly dangerous is the ingress of moisture on the surface of the turbine flow path in the presence of deposits of sodium compounds on them.
6.1.2. Preservation of the turbine unit with heated air is carried out when it is put into reserve for a period of 7 days or more.
Mothballing is carried out in accordance with the guidelines "Guidelines for Mothballing Steam Turbine Equipment at TPPs and NPPs with Heated Air: MU 34-70-078-84" (Moscow: SPO Soyuthenergo, 1984).
6.1.3. If the power plant does not have a conservation installation up to now, it is necessary to use mobile fans with an air heater to supply heated air to the turbine installation. Air can be supplied both to the entire turbine plant, and at least to its individual parts (central pressure center, low pressure cylinder, boilers, to the upper or lower part of the condenser or to the middle part of the turbine).
To connect a mobile fan, it is necessary to provide for the installation of an inlet valve.
To calculate the fan and inlet valve, recommendations MU 34-70-078-34 can be used.
When using mobile fans, drainage and vacuum drying measures specified in MU 34-70-078-84 should be carried out.
6.2. Preservation with nitrogen
6.2.1. When filling the internal cavities of the turbine unit with nitrogen and maintaining its small excess pressure in the future, the ingress of moist air is prevented.
6.2.2. Filling is carried out when the turbine plant is put into reserve for 7 days or more at those power plants where there are oxygen plants producing nitrogen with a concentration of at least 99%.
6.2.3. To carry out conservation, it is necessary to have a gas supply to the same points as air.
Consideration should be given to the difficulties of sealing the turbine flow path and the need to ensure the nitrogen pressure at the level of 5-10 kPa.
6.2.4. The supply of nitrogen to the turbine begins after the turbine is stopped and the vacuum drying of the reheater is completed.
6.2.5. Nitrogen conservation can also be used for the steam spaces of boilers and heaters.
6.3. Preservation with volatile corrosion inhibitors
6.3.1. Volatile corrosion inhibitors of the IFKHAN type protect steel, copper, brass by adsorbing on the metal surface. This adsorbed layer significantly reduces the rate of electrochemical reactions leading to the corrosion process.
6.3.2. To preserve the turbine, air saturated with an inhibitor is sucked in through the turbine. Air is sucked through the turbine using a seal ejector or a starting ejector. Air saturation with an inhibitor occurs when it comes into contact with silica gel impregnated with an inhibitor, the so-called linasil. Linasil is impregnated at the factory. To absorb excess inhibitor at the outlet of the turbine unit, the air is passed through pure silica gel.
Conservation with a volatile inhibitor is carried out when withdrawn to the reserve for a period of more than 7 cy.
6.3.3. To fill the turbine with inhibited air at the inlet to it, for example, a cartridge with linasil is connected to the steam supply pipeline to the front seal of the HPC (Fig. 5). To absorb the excess inhibitor at the outlet of the equipment, cartridges with pure silica gel are installed, the volume of which is 2 times the volume of linasil at the inlet. In the future, this silica gel can be additionally impregnated with an inhibitor and, during the next preservation, installed at the inlet to the equipment.
Fig. 5. Turbine conservation with volatile inhibitor:
1 - main steam valve; 2 - high pressure stop valve;
3 - high pressure control valve; 4 - medium safety valve
pressure; 5 - medium pressure control valve; 6 - suction chambers
steam-air mixture from the end seals of the cylinders;
7 - sealing steam chamber; 8 - pipeline of sealing steam;
9 - existing valves; 10 - collector of vapor-air mixture for seals;
11 - collector for suction of the steam-air mixture; 12 - supply pipeline
inhibitor; 13 - cartridge with linasil; 14 - newly mounted gate valves;
15 - ejector of seals; 16 - exhaust to atmosphere; 17 - cartridges with clean
silica gel to absorb the inhibitor; 18 - suction pipeline
steam-air mixture from chambers; 19 - intermediate superheater;
20 - air sampling; 21 - flange; 22 - gate valve
To fill the turbine with inhibited air, standard equipment is used - a seal ejector or a starting ejector.
To preserve 1 m3 of volume, at least 300 g of linasil is required, the protective concentration of the inhibitor in the air is 0.015 g / dm3.
Linasil is placed in cartridges, which are pieces of pipes, to both ends of which flanges are welded. Both ends of the pipe with flanges are tightened with a mesh with a mesh size that does not allow linasil to spill out, but does not interfere with the passage of air. The length and diameter of the pipes is determined by the amount of linasil required for conservation.
Linasil is loaded into cartridges with a spatula or with gloved hands.
6.3.4. Before the start of conservation, in order to exclude possible accumulation of condensate in the turbine, pipelines and valves, they are drained, the turbine and its auxiliary equipment are de-steam, disconnected from all pipelines (drains, steam extraction, steam supply to the seals, etc.).
To remove the possible accumulation of condensate in the undrained areas, the turbine is dried with air. To do this, a cartridge with calcined silica gel is installed at the inlet and an ejector sucks air along the circuit "cartridge-HPC-CDC-LPC-collector for suction of the vapor-air mixture from the seals-ejector-atmosphere".
After the turbine metal has cooled down to approximately 50 ° C, it is sealed with a packing of asbestos impregnated with a sealant at the air inlet from the turbine room to the suction chamber of the vapor-air mixture of the end seals.
After drying the turbine, cartridges with linasil are installed at the inlet, and cartridges with pure silica gel are installed at the outlet, the ejector is turned on and air is sucked along the contour "cartridge-pipeline for supplying steam to the seal-HPC-collector for suction of the steam-air mixture-cartridges with silica gel-ejector-atmosphere". When the protective concentration of the inhibitor, equal to 0.015 g / dm3, is reached, the conservation stops, for which the ejector is turned off, a plug is installed at the air inlet to the linasil cartridge and at the inlet of inhibited air to the silica gel cartridges.
6.3.5. During the period when the turbine is in reserve, the inhibitor concentration in it is determined monthly (Appendix 2).
When the concentration drops below 0.01 g / dm 3, re-preservation with fresh linasil is carried out.
6.3.6. To de-preserve the turbine, the cartridges with linasil are removed, the plug at the inlet of inhibited air to the cartridge with silica gel, the ejector is turned on, and the inhibited air is drawn through the silica gel to absorb the remaining inhibitor for the same time that it took to preserve the turbine.
Since the conservation is carried out in a closed circuit, there are no effluents or emissions into the atmosphere.
Brief characteristics of the chemicals used are given in Appendix 3.
RD 34.20.593-89
INSTRUCTIONS
ON THE APPLICATION OF CALCIUM HYDROXIDE FOR PRESERVATION
HEAT POWER AND OTHER INDUSTRIAL EQUIPMENT
AT THE OBJECTS OF THE USSR MINISTRY OF ENERGY
Valid from 01/01/89
until 01.01.99 *
__________________
* For the expiration date, see the "Notes" label. -
Database manufacturer's note.
WORKED BY the All-Union Intersectoral Research Institute for the Protection of Metals from Corrosion, the REU "Mosenergo", the 1st Moscow Order of Lenin and the Order of the Red Banner of Labor Medical Institute. I.M.Sechenov
CONTRACTORS A.P. AKOLZIN (All-Union Intersectoral Research Institute for the Protection of Metals from Corrosion), G. A. SHCHAVELEVA (REU "Mosenergo"), Y. Y. KHARITONOV (1st MMI)
APPROVED by the Main Scientific and Technical Directorate of Energy and Electrification on 12/30/88
Deputy Head A.P. BERSENEV
These Guidelines set out a method for protecting heat and power equipment from parking corrosion when it is put into reserve, as well as during emergency and planned shutdowns.
Preservation with calcium hydroxide solution is used for any hot water boilers and for steam drum boilers with pressures up to 4.0 MPa that do not have superheaters, as well as for steam boilers with superheaters, but the superheaters themselves are not preserved.
The guidelines apply to stationary power plants, heating boiler houses, enterprises with hot water and steam power boilers with pressures up to 4.0 MPa, and must be taken into account by design organizations.
Based on these Guidelines, enterprises draw up local work instructions for conservation.
When preserving the equipment, it is necessary to observe the current "Safety Rules for the Operation of Thermal Mechanical Equipment of Power Plants and Heating Networks" (M .: Energoizdat, 1985), as well as the precautions set forth in Section 4.
1. CHARACTERISTIC OF THE METHOD FOR PRESERVATION OF HEAT POWER EQUIPMENT WITH CALCIUM HYDROXIDE
1. CHARACTERISTIC OF THE PRESERVATION METHOD
HEATING EQUIPMENT WITH CALCIUM HYDROXIDE
1.1. The method of protection against parking corrosion (conservation) of heat and power equipment, based on the use of inhibiting solutions of calcium hydroxide, is highly effective.
1.2. Calcium hydroxide (see reference annex) is a non-funded local product which makes it widely available. It is also a waste of a number of industries (for example, welding). Calcium hydroxide solutions are harmless to humans and the environment. When discharging waste solutions, it is required to dilute them with water to pH<8,5. Вследствие малой растворимости (около 1,4 г/л при 25 °С) создать
концентрации раствора гидроксида кальция, опасные для жизни и
здоровья человека, практически невозможно. Кроме того, в
естественных условиях (водоемах, почвах) происходит быстрая
нейтрализация гидроксида кальция путем его взаимодействия с
углекислым газом атмосферы, в результате чего образуется карбонат
кальция (мел), также безопасный для здоровья
человека.
1.3. The effectiveness of the protective action of calcium hydroxide solutions in relation to the metal of heat and power equipment in all respects is significantly higher than that of a number of other inhibitors.
For example, the corrosion rate of steel in the presence of calcium hydroxide (protective concentration, see clause 1.4) in environments containing up to 3 g / l of chlorides is 1.5-2.2 times lower than in sodium silicate solutions, and 10 -12 times lower than in sodium hydroxide solutions at the same equivalent concentration of inhibitors. The corrosion rate was determined gravimetrically and by the method of polarization resistance.
1.4. The protective concentration of calcium hydroxide solutions in relation to equipment made of carbon steel is 0.7 g / l and higher.
Overdose is impossible due to its limited solubility.
1.5. With prolonged conservation (more than a month) under conditions of contact of the preserving solution with air, its concentration gradually decreases due to the absorption of acidic components of the air. A decrease in pH to less than 8.3 is unacceptable, since it indicates the appearance of carbonates, bicarbonates and hydrosulfites in the preservative solution, i.e. products of interaction of calcium hydroxide with air components. The result of this interaction is a decrease in the protective effect. The control of the preservative solution is carried out by taking samples at least once a week. When the pH of the solution drops below the permissible level (the disappearance of the color for phenolphthalein), the preservative solution should be renewed.
In the absence of contact with air, the protective properties of the solution are not limited by time.
1.6. The presence of corrosion activators (chlorides in a concentration of up to 0.365 g / l and sulfates up to 0.440 g / l) in a calcium hydroxide solution with a concentration of 0.7 g / l and higher practically does not reduce the protective properties of preservative solutions. This is due to the fact that a phase protective film with a thickness of 12-21 μm is formed in calcium hydroxide solutions on the surface of carbon steel, consisting of insoluble hydroxo and aqua complexes of iron and calcium, which also includes other compounds and ions.
1.7. If bicarbonates are present in an aqueous preservative solution (when preparing a solution on river water), the protective properties of the films formed on steel increase due to the additional formation of calcium carbonate (chalk) layers.
1.8. The preservative solution is prepared in water with a temperature below 40 ° C, since as the temperature rises, the solubility of calcium hydroxide in water decreases and the protective properties of the solution decrease.
2. TECHNOLOGY OF PRESERVATION
2.1. Calcium hydroxide preservative solutions are prepared from milk of lime. At the WPU with pretreatment, you can use a lime solution prepared for clarifiers.
2.2. For the preparation of milk of lime, almost any slaked lime can be used, including construction lime, with preliminary removal of the undershot; fluff lime; waste quenching of calcium carbide in the production of acetylene. Slaked lime and milk of lime should not contain sand, clay and other contaminants insoluble in water (see clauses 2.5, 2.6, 2.8).
2.3. Preservative solutions are prepared on condensate or chemically purified water. Sea and boiler water is not suitable for the preparation of preservative solutions.
2.4. The preservative solution is prepared in a separate supply tank with a volume of 20-70 m. It is more convenient when the volume of the supply tank exceeds the volume of the equipment to be preserved. The amount of slaked lime supplied to the supply tank for the preparation of the preservative solution is 1-1.5 kg per 1 m of water in the tank. Preliminarily, lime is stirred with water to a liquid consistency, then the mixture is poured into the tank through a mesh with cells of no more than 1 mm to retain solid impurities.
2.5. In the tank, the preservative solution settles for 10-12 hours until the reagent is completely clarified and dissolved.
2.6. The preservative solution can be fed from the supply tank to the boiler by gravity. For this, the tank is installed above the boiler. If the supply tank is at the bottom, the boiler is filled with pumps.
2.7. The selection of preservative solutions is carried out not from the lowest point of the supply tank, but from a level of 40-50 cm from the bottom of the tank in order to avoid the ingress of solid insoluble particles into the boiler. For the same purpose, the preservative solutions are passed through any mechanical filter before being fed into the boiler.
2.8. The preservative solution is fed into a completely drained and cooled boiler. Preservation can be carried out both on a chemically or mechanically cleaned boiler, and on a boiler with internal deposits. The solution is fed through the lower collectors of the boiler.
2.9. The entire internal volume of the boiler is filled with a preservative solution. If a hot water boiler has a closed circulation loop, then the entire circuit, including pipelines and heat exchangers, is filled with a preservative solution. In drum boilers, water economizers, guard and downpipes and the boiler drum are filled.
2.10. If the amount of solution prepared in the supply tank is not enough to fill the entire boiler, the next portion of the preservative solution is prepared in the supply tank in accordance with paragraphs 2.4-2.8.
2.11. For hot water boilers, it is advisable to provide stationary systems for the preparation of preservative solutions and their supply to the boiler. Possible schemes for the preparation and supply of preservative solutions are shown in Figs. 1, 2. In Fig. 1, for the preparation of solutions, the scheme has a saturator tank. There is also a filter (for example, of the type of water treatment salt dissolver). Fig. 2 shows another variant of conservation, which provides for the supply of a preservative solution using the acid washing scheme for hot water boilers.
Fig. 1. Scheme of adding calcium hydroxide to canned equipment
Fig. 1. Scheme of introducing calcium hydroxide into canned equipment:
1 - filling funnel; 2 - lime milk preparation tank; 3 - preservative preparation tank
calcium hydroxide solution; 4 - filter; 5 - supply tank; 6 - ejector; 7 - feed pump; I - condensate;
II - chemically purified water; III - steam; IV - sampling before the introduction of calcium hydroxide; V - sampling after
calcium hydroxide injection; VI -
from the feed tanks; VII - for boilers
Fig. 2. Scheme of preservation of hot water boilers with Ca (OH) solution (2) using acid washing scheme
Fig. 2. Scheme for preserving hot water boilers with a solution using an acid washing scheme: If the payment procedure on the payment system website has not been completed,
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Russian joint stock company
energy and electrification "UES of Russia"
Department of Science and Technology
INSTRUCTIONS
FOR CONSERVATION
HEAT POWER EQUIPMENT
RD 34.20.591-97
Expiration date set
from 01.07.97 to 01.07.2002
Designed by company for the adjustment, improvement of technology and operation of power plants and networks "ORGRES" and JSC VTI
PerformersIN AND. Startsev (JSC "Firm ORGRES"), E.Yu. Kostrikina, T. D. Modestova (JSC VTI)
Approved byDepartment of Science and Technology of RAO "UES of Russia" 02/14/97
Head A.P. BERSENEV
These Guidelines apply to power and hot water boilers, as well as turbine installations of thermal power plants.
The methodological guidelines determine the main technological parameters of various conservation methods, establish criteria for choosing methods or combinations (combinations) of methods, the technology for their implementation on boilers and turbine plants when they are put into reserve or repair, taking into account a sharp increase in both the number of shutdowns and the duration of equipment downtime at power plants.
With the introduction of these Guidelines, the “Guidelines for the conservation of heat and power equipment: RD 34.20.591-87” (Moscow: Rotaprint VTI, 1990) are no longer valid.
1. GENERAL PROVISIONS
The water discharged from the boiler must be used in the steam-water cycle of the power plant, for which it is necessary to provide for pumping of this water to neighboring blocks at block power plants.
During processing, the hydrazine content is monitored by taking water samples from a sampling point on the feed water line in front of the boiler.
At the end of the specified processing time, the boiler is stopped. When stopping in reserve for a period of up to 10 days, the boiler may not be drained. In the event of a longer downtime, a CO should be performed after hydraulic fracturing.
At the end of the FV, the boiler is stopped and, after the pressure drops to atmospheric, it is emptied, directing the solution to neutralization.
2.7.8 ... The boiler, which has been withdrawn into the reserve and emptied, is filled with a preservative solution through the lower points of the screens and drainage E. The filling of the boiler is controlled by means of air vents.
If the solution is stirred in the boiler by recirculation (see Fig. 1), then the end of it is determined by equalizing the concentration of the solution at the sampling points along the steam-water path.
After filling the boiler, close all the shut-off valves of the steam-water path.
2.7.9 ... During the conservation period of the boiler, the tightness of the closure of valves and gates is regularly checked, leaks and leaks of glands are promptly eliminated.
In case of partial emptying, the boiler is fed with a fresh solution of reagents.
2.7.10 ... At the end of the conservation, the solution from the boiler is drained into the reagent tank, using, if necessary, to fill another preserved boiler or directing it to the neutralization unit.
If the boiler was preserved with a solution of caustic soda with trisodium phosphate, before firing up, the steam superheater is washed with water for 30 - 60 minutes with water being discharged through the lower points of the boiler. The superheater flushing line must be reliably disconnected from the operating boiler.
2.8. Filling the boiler heating surfaces with nitrogen
2.8.1 ... Filling the internal heating surfaces with chemically inert nitrogen followed by maintaining its excess pressure in the boiler prevents oxygen access, which ensures the stability of the previously formed protective film on the metal for a long time.
2.8.2 ... The boiler is filled with nitrogen at overpressure in the heating surfaces. During the conservation process, the nitrogen flow rate must ensure a slight overpressure in the boiler.
2.8.3 ... Nitrogen conservation is used on boilers of any pressure in power plants that have nitrogen from their own oxygen plants. In this case, it is allowed to use nitrogen at its concentration of at least 99%.
2.8.4 ... Filling with nitrogen is carried out when the boiler is put into reserve for a period of up to one year.
2.8.5 ... The conservation scheme should provide for the supply of nitrogen to the outlet headers of the superheaters and to the drum through the air vents.
The supply to the air vents is carried out by means of tie-in pipes with high-pressure fittings. The outlets from the air vents should be combined into a common collector, which is connected to the nitrogen supply pipeline. The collector that combines the branches from the air vents must be reliably disconnected from the nitrogen pipeline by installing high-pressure fittings. On this manifold, it is necessary to have an inspection valve open during the operation of the boiler.
The specific layout of the nitrogen pipelines is developed taking into account the capabilities of the oxygen plant and the types of installed boilers.
2.8.6 ... When the boiler is shut down for up to 10 days, conservation is carried out without draining the water from the heating surfaces.
After stopping the boiler and reducing the pressure in the drum to 0.2-0.5 MPa, open the valves on the nitrogen supply lines to the superheater and to the drum and proceed, if necessary, to drain the boiler, after which the drains are closed.
During the conservation process, the gas pressure in the boiler is maintained at the level of 5 - 10 kPa.
2.8.7 ... During the conservation period, measures are taken to identify possible gas leaks and eliminate them.
2.8.8 ... If it is necessary to carry out minor repairs, a short-term interruption of the gas supply to the boiler is possible.
2.9. Preservation of the boiler with a contact inhibitor
2.9.1 ... Contact inhibitor M-1 is a salt of cyclohexylamine and synthetic fatty acids.
In the form of an aqueous solution, a contact inhibitor (KI) protects cast iron and steel of various grades against corrosion. Its protective properties are due to the presence of amino groups in the inhibitor in the hydrophobic part of the molecule. Upon contact with the metal surface, the inhibitor is adsorbed at the amino group, leaving the hydrophobic part of the molecule in the external environment. This structure of the adsorption layer prevents the penetration of moisture or electrolyte to the metal. An additional obstacle is the overlying layers of inhibitor molecules, which enhance the adsorption layer. Water and gas molecules penetrating deep into this layer ( S О 2, СО 2, etc.) lead to hydrolysis of a part of the inhibitor molecule. This liberates cyclohexylamines and fatty acids. Cyclohexylamines bind acid gases, and acids, being adsorbed, maintain the hydrophobicity of the metal surface.
The contact inhibitor creates a protective film on the metal, which remains even after the preservative solution has been drained.
2.9.2 ... To preserve the heating surfaces, the boiler is filled with an aqueous solution of an inhibitor with a concentration of 0.5 - 1.5%, depending on the duration of the downtime, the composition and the amount of deposits on the heating surfaces. The specific concentration of the inhibitor solution is established after a chemical analysis of the composition of the deposits.
2.9.3 ... KI conservation is used for all types of boilers, regardless of the applied modes of corrective treatment of feed and boiler water.
2.9.4 ... Preservation with M-1 inhibitor is carried out when the boiler is taken into reserve or under repair for a period of 1 month or more. up to 2 years.
2.9.5 ... To carry out conservation, a special separate scheme for preparing an aqueous solution of the inhibitor and feeding it into the boiler should be provided (Fig. 3). The scheme includes a tank for storing and preparing a solution with a capacity of at least the full water volume of the boiler and a pump for mixing the solution and supplying it to the boiler. The tank must be supplied with condensate or demineralized water.
The boiler is filled with an inhibitor solution through the pipeline from the pressure side of the pump to the lower drainage header of the boiler. Through the same pipeline, the preservative solution from the boiler is discharged into the storage tank during re-preservation.
2.9.6 ... To prepare a working solution, flasks with a commercial inhibitor are preheated by dropping them into a bath with water heated to 70 ° C. The approximate warm-up time is 8 - 10 hours.
The heated commercial inhibitor is poured into the tank of the preservative solution during water recirculation according to the "tank - pump - tank" scheme. The circulating water temperature should be around 60 ° C. The circulation time of the solution is 1 h. The concentration of the inhibitor in the working solution is determined in accordance with the application procedure.
Vdovenko Denis Yurievich - technical director
Zaporozhtsev Valery Anatolyevich - head of the laboratory
Possokhov Artem Igorevich - specialist in non-destructive testing
Expert organization LLC "Teploenergo", Rostov-on-Don
The article provides recommendations for the conservation of steam boilers in drum and direct-flow design, depending on the design features, reasons and timing of equipment downtime. The mechanism of metal parking corrosion and its consequences is considered.
Key words: thermal power plant, parking corrosion, conservation, hazardous production facility, steam boiler, safety.
Compliance with the requirements of the "Rules for the technical operation of thermal power plants" and safety rules requires organizations operating thermal power plants to preserve thermal power equipment in the following cases:
- during operational shutdowns of equipment (withdrawal to the reserve for a certain and indefinite period, withdrawal to current and major repairs, emergency shutdown);
- in case of equipment shutdowns in a long-term reserve or repair (reconstruction) for a period of more than 6 months;
- at the end of the heating season or during a shutdown, water heating boilers and heating systems are preserved.
Preservation of steam boilers during their downtime provides for a set of organizational and technical measures aimed at maintaining the operating condition of the equipment by preventing corrosion on its surface, extending the service life, as well as reducing the cost of repairing and restoring equipment in the future.
According to the requirements of the rules, the organization operating the steam boiler must develop and approve a technical solution for its conservation. In order to comply with the requirements of the law on industrial safety, documentation for the conservation of a hazardous production facility is subject to an industrial safety examination.
Technical solutions for conservation should contain:
- methods of preservation of boilers during various types of shutdowns and downtime;
- technological scheme of conservation;
- a list of auxiliary equipment by means of which conservation is carried out.
On the basis of technical solutions, instructions for the preservation of the steam boiler are drawn up and approved. In turn, the preservation instructions should contain:
- preparatory operations performed prior to conservation;
- technology of steam boiler conservation;
- technology for de-mothballing a steam boiler;
- security measures during work.
From a technical point of view, the preservation of boilers is necessary to prevent the occurrence of parking corrosion of the metal. Standing corrosion occurs as a result of the aggressive action of oxygen in the air in contact with the wet metal surface of the boiler during its inactivity. In other words, parking corrosion is a type of oxygen corrosion, the mechanism of which can be described according to a chemical reaction:
4Fe + 6Н 2 О + 3О 2 = 4Fe (OH) 3 (1)
It is possible to distinguish standing corrosion from other types of corrosion by the presence of characteristic pits and the accumulation of corrosion products on the metal surface (Figure 1), which form under the deposits of sludge, which contains a greater amount of moisture after the boiler water is drained.
Figure 1 - Standing corrosion.
Methods for preserving drum steam boilers:
- dry shutdown of the boiler (CO);
- maintaining overpressure in the boiler;
- filling the boiler heating surfaces with nitrogen (A);
- hydrazine treatment (GO) of heating surfaces at reduced boiler parameters;
- Trilon treatment (TO) of the boiler heating surfaces;
- phosphate-ammonia "evaporation" (FV);
- filling the boiler heating surfaces with protective alkaline solutions;
- preservation of the boiler with a contact inhibitor (CI).
Methods for conservation of once-through steam boilers:
- dry shutdown of the boiler;
- filling the boiler heating surfaces with nitrogen;
- hydrazine treatment of heating surfaces at the operating parameters of the boiler;
- preservation of the boiler with a contact inhibitor.
The dry shutdown method of preserving a steam boiler is based on the principle of keeping the inner surface of the equipment dry for the entire preservation period. It is carried out by draining the boiler at a pressure above atmospheric (0.8 - 1.0 MPa), which allows drying the inner surfaces of the drum, collectors and pipes due to the heat accumulated by the metal, lining and insulation of the boiler. To prevent the ingress of moisture, steam and water pipelines are disconnected from the boiler by tightly closing the shut-off valves and installing plugs. After the boiler has completely cooled down, it is necessary to periodically ensure that water or steam does not enter the boiler, for this it is necessary from time to time to briefly open the drains at the lowest points of the collectors and pipelines.
The preservation method by maintaining overpressure in the boiler is based on the principle of preventing the penetration of air oxygen into the boiler. After stopping the boiler and reducing the pressure to atmospheric, the water is drained from it, then they proceed to filling with preservative water and organizing its flow through the boiler. A mandatory requirement for conservation water is the removal of dissolved oxygen in the deaerator. During the conservation period, the boiler maintains a pressure of 0.5 - 1.5 MPa and a water flow at a rate of 10 - 30 m 3 / h. Control over the oxygen content in the conservation water is carried out by monthly sampling from the clean and salt compartments of the superheater.
The conservation method by filling the boiler heating surfaces with nitrogen and maintaining an overpressure in the boiler prevents oxygen access and ensures the formation of a protective film on the metal surface. If the boiler is shut down for up to 10 days, the preservation of the heating surface with nitrogen can be carried out without draining the boiler water. If the shutdown presupposes a longer conservation period, the water must be drained from the boiler. Nitrogen is supplied to the boiler through the superheater outlet headers and drum air vents. The gas pressure during storage must be maintained at a level of 5 - 10 kPa.
The remaining methods of preservation of steam boilers can be combined into one large group - wet preservation. Their principle is based on filling the boiler with a preservative solution, which ensures the formation of a protective film on the surface of the boiler for a long time, in some cases the protective film is resistant when oxygen enters the boiler. The preparation of the preservative solution of the reagents is carried out in the tank, the solution is supplied to the boiler using a metering pump. The preparation of the preservative solution of the required concentration is carried out in accordance with the approved methods.
When choosing a method for preserving a steam drum boiler, it is recommended to use table 1.
Notes:
1. On boilers with a pressure of 9.8 MPa without treatment of feed water with hydrazine, maintenance should be carried out at least once a year.
2.A - filling the boiler heating surfaces with nitrogen.
3. Hydraulic fracturing + CO - hydrazine treatment at the operating parameters of the boiler, followed by dry shutdown; GO + ZSch, TO + ZSh, FV + ZSh - filling the boiler with an alkaline solution with previous reagent treatment.
4. TO + CI ( preservation with contact inhibitor with prior trilon treatment).
5. “Before”, “after” - before and after renovation.
When preserving a once-through steam boiler, it is recommended:
1. In case of shutdown for up to 30 days, preserve by dry shutdown of the boiler.
2. In case of putting the boiler into reserve for a period of up to 3 months or repairs for a period of up to 5 - 6 months, carry out hydrazine or oxygen treatment in combination with a dry shutdown of the boiler.
3. In the case of longer periods of reserve or repair, the boiler conservation should be carried out using a contact inhibitor or by filling the boiler heating surfaces with nitrogen.
Table 1 - Methods of preservation of drum steam boilers
depending on the type and duration of the downtime.
conclusions:
1. Preservation of the steam boiler during its downtime is carried out in order to prevent the development of parking corrosion of the metal.
2. Methods for preventing parking corrosion are based on the principles:
- exclusion of contact of oxygen in the air with the metal surface of the equipment;
- ensuring the metal surface in a dry state;
- creating a protective film on the metal surface or the corrosion-protective composition of water.
3. When choosing a method of conservation of steam boilers, it is necessary to take into account: the reason for putting the equipment into storage, the duration of the planned downtime of the equipment, design features of the equipment based on the passport data.
4. Documentation for the conservation of a hazardous production facility is subject to an industrial safety examination.
Bibliography:
1. Rules for the technical operation of thermal power plants. Approved. by order of the Ministry of Energy of the Russian Federation of March 24, 2003 N 115.
2 Federal norms and rules in the field of industrial safety "Rules of industrial safety of hazardous production facilities where equipment operating under excessive pressure is used". Approved. by order of Rostekhnadzor dated 03.25.2014 N 116.
