If the boiler is stopped for a long time, it must be mothballed. When preserving boilers, you must follow the manufacturer's instructions for installation and operation.
To protect boilers from corrosion, dry, wet and gas preservation methods are used, as well as, in some cases, preservation using the overpressure method.
The dry preservation method is used when the boiler is stopped for a long time and when it is impossible to heat the boiler room in winter. Its essence lies in the fact that after removing water from the boiler, superheater and economizer and cleaning the heating surfaces, the boiler is dried by passing hot air (thorough ventilation) or by lighting a small fire in the firebox. In this case, the safety valve must be open to remove water vapor from the drum and pipes. If a superheater is installed, the drain valve on the superheated steam chamber must be opened to remove any remaining water. After drying is completed, pre-prepared iron trays with quicklime CaO or silica gel (in the amount of 0.5-1.0 kg CaC12, 2-3 kg CaO or 1.0-1.5 kg silica gel per 1 m3) are placed through open holes in the drums boiler volume). The openings of the drum are tightly closed and all fittings are covered. When stopping the boiler for more than 1 year, it is recommended to remove all fittings and install plugs on the fittings. In the future, the condition of the reagents must be checked at least once a month, and then every 2 months, depending on the results of the check, it must be replaced. It is recommended to periodically monitor the condition of the lining and, if necessary, dry it.
Wet method. Wet preservation of boilers is used when there is no danger of water freezing in them. Its essence lies in the fact that the boiler is completely filled with water (condensate) with high alkalinity (caustic soda content 2-10 kg/m3 or triphosphate 5-20 kg/m3). Then the solution is heated to boiling temperature to remove from air and dissolved gases and tightly close the boiler. The use of an alkaline solution ensures sufficient stability at a uniform concentration protective film on the metal surface.
Gas method. At gas method preserved water is drained from the cooled boiler and the internal heating surface is thoroughly cleaned of scale. After this, the boiler is filled with ammonia gas through the air vent and a pressure of about 0.013 MPa (0.13 kgf/cm2) is created. The effect of ammonia is that it dissolves in the film of moisture that is on the surface of the metal in the boiler. This film becomes alkaline and protects the boiler from corrosion. With the gas method, the personnel carrying out preservation must know the safety rules.
The overpressure method consists in maintaining the steam pressure slightly higher than atmospheric and the water temperature above 100 °C in the boiler, disconnected from the steam lines. This prevents air, and therefore oxygen, which is the main corrosive agent, from entering the boiler. This is achieved by periodically heating the boiler.
When the boiler is put into cold reserve for up to 1 month, it is filled with deaerated water and a slight excess hydrostatic pressure is maintained in it by connecting it to a tank with deaerated water located above. However, this method is less reliable than the previous one.
With all methods of preserving boilers, it is necessary to ensure complete tightness of the fittings; all hatches and manholes must be tightly closed; with the dry and gas method, non-working boilers must be separated from working boilers with plugs. Preservation of equipment and its control are carried out according to special instructions and under the guidance of a chemist.
If the boiler is stopped for a long time, it must be mothballed. When preserving boilers, you must follow the manufacturer's instructions for installation and operation.
To protect boilers from corrosion, dry, wet and gas preservation methods are used, as well as, in some cases, preservation using the overpressure method.
Dry method conservation is used when the boiler is stopped for a long time and when it is impossible to heat the boiler room in winter. Its essence lies in the fact that after removing water from the boiler, superheater and economizer and cleaning the heating surfaces, the boiler is dried by passing hot air (thorough ventilation) or by lighting a small fire in the firebox. In this case, the safety valve must be open to remove water vapor from the drum and boiler pipes. If a superheater is installed, the drain valve on the superheated steam chamber must be opened to remove any remaining water. After drying is completed, pre-prepared iron trays with quicklime CaO or silica gel (in the amount of 0.5-1.0 kg CaC12, 2-3 kg CaO or 1.0-1.5 kg silica gel per 1 m3) are placed through open holes in the drums boiler volume). The openings of the drum are tightly closed and all fittings are covered. When stopping the boiler for more than 1 year, it is recommended to remove all fittings and install plugs on the fittings. In the future, the condition of the reagents must be checked at least once a month, and then every 2 months, depending on the results of the check, it must be replaced. It is recommended to periodically monitor the condition of the lining and, if necessary, dry it.
Wet method. Wet preservation of boilers is used when there is no danger of water freezing in them. Its essence lies in the fact that the boiler is completely filled with water (condensate) with high alkalinity (caustic soda content 2-10 kg/m3 or triphosphate 5-20 kg/m3). Then the solution is heated to boiling temperature to remove remove air and dissolved gases and close the boiler tightly.The use of an alkaline solution ensures, at a uniform concentration, sufficient stability of the protective film on the metal surface.
Gas method. With the gas preservation method, water is drained from the cooled boiler and the internal heating surface is thoroughly cleaned of scale. After this, the boiler is filled with ammonia gas through the air vent and a pressure of about 0.013 MPa (0.13 kgf/cm2) is created. The effect of ammonia is that it dissolves in the film of moisture that is on the surface of the metal in the boiler. This film becomes alkaline and protects the boiler from corrosion. With the gas method, the personnel carrying out preservation must know the safety rules.
Overpressure method lies in the fact that in a boiler disconnected from the steam lines, the steam pressure is maintained slightly above atmospheric and the water temperature is above 100 ° C. This prevents air, and therefore oxygen, which is the main corrosive agent, from entering the boiler. This is achieved by periodically heating the boiler.
When the boiler is put into cold reserve for up to 1 month, it is filled with deaerated water and a slight excess hydrostatic pressure is maintained in it by connecting it to a tank with deaerated water located above. However, this method is less reliable than the previous one.
With all methods of preserving boilers, it is necessary to ensure complete tightness fittings; all hatches and manholes must be tightly closed; with the dry and gas method, non-working boilers must be separated from working boilers with plugs. Preservation of equipment and its control are carried out according to special instructions and under the guidance of a chemist.
You can order products for preservation of boilers and equipment from us!
5. METHODS OF PRESERVATION OF WATER BOILERS
5.1. Preservation with calcium hydroxide solution
5.1.1. The method is based on the highly effective inhibitory abilities of calcium hydroxide solution Ca(OH).
The protective concentration of calcium hydroxide is 0.7 g/kg and above.
When a calcium hydroxide solution comes into contact with metal, a stable protective film is formed within 3-4 weeks.
When the boiler is emptied of solution after contact for 3-4 weeks or more, the protective effect of the films remains for 2-3 months.
This method is regulated " Guidelines on the use of calcium hydroxide for the conservation of thermal energy and other industrial equipment at the facilities of the Ministry of Energy RD 34.20.593-89" (M.: SPO Soyuztekhenergo, 1989).
5.1.2. When implementing this method, the water heating boiler is completely filled with solution. If it is necessary to carry out repair work, solution after aging in the boiler for 3-4 weeks. may be drained.
5.1.3. Calcium hydroxide is used for the preservation of hot water boilers of any type at power plants that have water treatment plants with lime facilities.
5.1.4. Preservation with calcium hydroxide is carried out when the boiler is put into reserve for a period of up to 6 months or put into repair for a period of up to 3 months.
5.1.5. The calcium hydroxide solution is prepared in wet lime storage cells with a floating suction device (Fig. 4). After adding lime (fluff, building lime, calcium carbide slaking waste) into the cells and mixing, the milk of lime is allowed to stand 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. Preservation scheme for hot water boilers:
1 - tank for preparing chemical reagents; 2 - boiler filling pump
a solution of chemical reagents; 3 - make-up water; 4 - chemical reagents;
5 - lime milk into pre-cleaning mixers, 6 - lime milk cells;
7 - hot water boilers; 8 - to other hot water boilers;
9 - from other hot water boilers;
preservation pipelines
When pumping solution out of the cell, it is necessary to monitor the position of the floating suction device to avoid trapping sediments at the bottom of the cell.
5.1.6. To fill the boilers with the solution, it is advisable to use the acid washing scheme for hot water boilers shown in Fig. 4. A tank with a pump can also be used to preserve energy boilers (see Fig. 2).
5.1.7. Before filling the boiler with a preservative solution, the water from it is drained.
A solution of calcium hydroxide from lime cells is pumped into the reagent preparation tank. Before pumping, the pipeline is washed with water to prevent lime milk supplied through this pipeline for pre-treatment of the water treatment plant from entering the tank.
It is advisable to fill the boiler by recirculating the solution along the “tank-pump-solution supply pipeline-boiler-solution discharge pipeline-tank” circuit. In this case, the amount of cooked lime mortar should be sufficient to fill the preserved boiler and recirculation circuit, including the tank.
If the boiler is filled by a pump from the tank without organizing recirculation through the boiler, then the volume of lime milk prepared depends on the water volume of the boiler.
The water volume of the PTVM-50, PTVM-100, PTVM-180 boilers is 16, 35 and 60 m respectively.
5.1.8. When put into reserve, the boiler is left filled with solution for the entire idle time.
5.1.9. If it is necessary to carry out repair work, drainage of the solution is carried out after soaking in the boiler for at least 3-4 weeks in such a way that after the completion of the repair the boiler is put into operation. It is advisable that the duration of the repair does not exceed 3 months.
5.1.10. If the boiler is left with a preservative solution during downtime, it is necessary to monitor the pH value of the solution at least once every two weeks. To do this, recirculate the solution through the boiler and take samples from the 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 washed with network water until the wash water is hard, having previously drained it if it was filled with 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 the effects of corrosive agents (CO and O).
5.2.2. When implementing this method, the hot water 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 hot water boilers of all types.
5.2.4. Preservation with sodium silicate is carried out when the boiler is put into reserve for a period of up to 6 months or when the boiler is taken out for repairs for a period of up to 2 months.
5.2.5. To prepare and fill the boiler with sodium silicate solution, it is advisable to use the scheme for acid washing of hot water boilers (see Fig. 4). A tank with a pump can also be used to preserve energy boilers (see Fig. 2).
5.2.6. A sodium silicate solution is prepared using softened water, since the use of water with a hardness higher than 3 mEq/kg can lead to the precipitation of sodium silicate flakes from the solution.
The preservative solution of sodium silicate is prepared in a tank by circulating water according to the “tank-pump-tank” scheme. Liquid glass pours 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 volume of preservative solution.
5.2.8. Before filling the boiler with a preservative solution, the water from it is drained.
The working concentration of SiO in the preservative solution should be 1.5-2 g/kg.
It is advisable to fill the boiler by recirculating the solution along the “tank-pump-solution supply pipeline-boiler-solution discharge pipeline-tank” circuit. 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 just 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 clause 5.1.7).
5.2.9. When put into reserve, the boiler is left filled with a preservative solution for the entire idle time.
5.2.10. If it is necessary to carry out repair work, drainage of the solution is carried out after soaking in the boiler for at least 4-6 days in such a way that after completion of the repair the boiler is put into operation.
The solution can be drained from the boiler for repairs after circulating the solution through the boiler for 8-10 hours at a speed of 0.5-1 m/s.
The duration of repairs should not exceed 2 months.
5.2.11. If the boiler is left with a preservative solution during downtime, an excess pressure of 0.01-0.02 MPa is maintained in it with network water by opening the bypass valve at the inlet to the boiler. During the conservation period, samples are taken from the air vents once a week to monitor the concentration of SiO in the solution. When the SiO concentration decreases to less than 1.5 g/kg, add required amount liquid sodium silicate and recirculate the solution through the boiler until the required concentration is achieved.
5.2.12. The hot water boiler is re-preserved before it is fired by displacing the preservative solution into the network water pipelines in small portions (by partially opening the valve at the outlet of the boiler) at a rate of 5 m/h for 5-6 hours for the PTVM-100 boiler and 10-12 hours for the PTVM boiler -180.
At open systems heating supply, the displacement of the preservative solution from the boiler must take place without exceeding the MPC standards - 40 mg/kg SiO in network water.
6. METHODS OF PRESERVATION OF TURBINE UNITS
6.1. Preservation with heated air
6.1.1. Blowing the turbine unit with hot air prevents it from entering the internal cavities. humid air and the occurrence of corrosion processes. Moisture ingress on the surfaces of the turbine flow part is especially dangerous if there are deposits of sodium compounds on them.
6.1.2. Preservation of a turbine unit with heated air is carried out when it is put into reserve for a period of 7 days or more.
Conservation is carried out in accordance with the instructions "Methodological instructions for the conservation of steam turbine equipment of thermal power plants and nuclear power plants with heated air: MU 34-70-078-84" (M.: SPO Soyutekhenergo, 1984).
6.1.3. If the power plant does not currently have a conservation installation, it is necessary to use mobile fans with a heater to supply heated air to the turbine unit. Air can be supplied to the entire turbine installation, or at least to its individual parts (DCS, LPC, 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 install an inlet valve.
To calculate the fan and inlet valve, the recommendations of 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. Nitrogen preservation
6.2.1. By filling the internal cavities of the turbine unit with nitrogen and subsequently maintaining a small excess pressure, the ingress of moist air is prevented.
6.2.2. Filling is carried out when the turbine unit 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 the air.
It is necessary to take into account the difficulties of sealing the turbine flow path and the need to ensure nitrogen pressure at a level of 5-10 kPa.
6.2.4. The supply of nitrogen to the turbine begins after the turbine is stopped and vacuum drying intermediate superheater.
6.2.5. Nitrogen preservation can also be used for steam spaces of boilers and preheaters.
6.3. Preservation with volatile corrosion inhibitors
6.3.1. Volatile corrosion inhibitors of the IFKHAN type protect steel, copper, and brass by adsorbing on the metal surface. This adsorbed layer significantly reduces the rate of electrochemical reactions that cause the corrosion process.
6.3.2. To preserve the turbine unit, air saturated with the inhibitor is sucked through the turbine. Air is drawn through the turbine unit using a seal ejector or starting ejector. Saturation of the air with the inhibitor occurs when it comes into contact with silica gel impregnated with the inhibitor, the so-called linasil. Impregnation of linasil is carried out at the manufacturer. To absorb excess inhibitor, the air at the outlet of the turbine unit passes through pure silica gel.
Preservation with a volatile inhibitor is carried out when placed in reserve for a period of more than 7 days.
6.3.3. To fill the turbine with inhibited air at its inlet, for example, a cartridge with linasil is connected to the steam supply pipeline to the front seal of the HPC (Fig. 5). To absorb excess inhibitor, cartridges with pure silica gel are installed at the outlet of the equipment, the volume of which is 2 times greater than the volume of linasil at the inlet. In the future, this silica gel can be additionally impregnated with an inhibitor and installed at the entrance to the equipment during the next conservation.
Fig.5. Preservation of turbines with a volatile inhibitor:
1 - main steam valve; 2 - stop valve high pressure;
3 - high pressure control valve; 4 - middle 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 - sealing steam pipeline;
9 - existing valves; 10 - manifold of steam-air mixture for seals;
11 - steam-air mixture suction manifold; 12 - supply pipeline
inhibitor; 13 - cartridge with linasil; 14 - newly mounted valves;
15 - seal ejector; 16 - exhaust into the 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 - valve
To fill the turbine with inhibited air, standard equipment is used - a seal ejector or a starting ejector.
To preserve 1 m of volume, at least 300 g of linasil is required, the protective concentration of the inhibitor in the air is 0.015 g/dm.
Linasil is placed in cartridges, which are sections of pipes with flanges welded to both ends. Both ends of the pipe with flanges are tightened with a mesh with a mesh size that prevents the laminate from spilling out, but does not interfere with the passage of air. The length and diameter of the pipes are determined by the amount of linasil required for preservation.
Linasil is loaded into the cartridges with a spatula or gloved hands.
6.3.4. Before conservation begins, to eliminate possible accumulation of condensate in the turbine, pipelines and valves, they are drained, the turbine and its auxiliary equipment are de-steamed, and disconnected from all pipelines (drains, steam extraction, steam supply to seals, etc.).
To remove possible accumulation of condensate in undrained areas, the turbine is dried with air. To do this, a cartridge with calcined silica gel is installed at the inlet and air is sucked through the ejector along the circuit “cartridge-HPC-DCS-LPC-collector for suction of the steam-air mixture from the seals-ejector-atmosphere”.
After the turbine metal has cooled to approximately 50 °C, it is sealed with a packing of asbestos impregnated with sealant at the air inlet from the turbine room into the suction chamber of the steam-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 through the circuit “cartridge-pipeline for supplying steam to the seal-HPC-manifold for suction of the steam-air mixture-cartridges with silica gel-ejector-atmosphere”. When a protective inhibitor concentration of 0.015 g/dm is reached, conservation is terminated, for which the ejector is turned off, a plug is installed at the air inlet into the cartridge with linasil and at the entrance of inhibited air into the cartridges with silica gel.
6.3.5. While the turbine is in reserve, the inhibitor concentration in it is determined monthly (Appendix 2).
When the concentration drops below 0.01 g/dm, re-preservation is carried out with fresh linasil.
6.3.6. To re-preserve the turbine, remove the cartridges with linasil, remove the plug at the entrance of the inhibited air into the cartridge with silica gel, turn on the ejector, and the inhibited air is drawn through the silica gel to absorb the remaining inhibitor during the same time it took to preserve the turbine.
Since conservation is carried out in a closed circuit, there are no discharges or emissions into the atmosphere.
Brief characteristics the chemical reagents used are given in Appendix 3.
Vdovenko Denis Yurievich – technical director
Zaporozhtsev Valery Anatolyevich – head of the laboratory
Posokhov Artem Igorevich – non-destructive testing specialist
Expert organization Teploenergo LLC, Rostov-on-Don
The article provides recommendations for the preservation of steam boilers in drum and once-through designs, 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, stop corrosion, conservation, hazardous production facility, steam boiler, safety.
Compliance with the requirements of the “Rules for the Technical Operation of Thermal Power Installations” and safety rules requires organizations operating thermal power plants to preserve thermal power equipment in the following cases:
− during regime shutdowns of equipment (putting into reserve for a definite and indefinite period, putting into current and major renovations, Emergency Stop) ;
− when equipment is stopped for long-term reserve or repair (reconstruction) for a period of more than 6 months;
− upon completion heating season or when stopped, water heating boilers and heating networks are mothballed.
Preservation of steam boilers during their downtime involves a set of organizational and technical measures aimed at maintaining the operating condition of the equipment by preventing corrosion on its surface, extending its service life, and also reducing the cost of repair and restoration of 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 industrial safety examination.
Technical solutions for conservation must contain:
− methods for preserving boilers during various types shutdowns and downtime duration;
− technological scheme of conservation;
− list of auxiliary equipment through which conservation is carried out.
Based on technical solutions, instructions for preserving the steam boiler are drawn up and approved. In turn, the conservation instructions should contain:
− preparatory operations performed before conservation;
− steam boiler preservation technology;
− steam boiler re-preservation technology;
− safety measures during work.
From a technical point of view, conservation of boilers is necessary to prevent the occurrence of standstill corrosion of the metal. Parking corrosion occurs as a result of the aggressive action of oxygen in the air in contact with wet metal surface boiler during its downtime. In other words, parking corrosion is a type of oxygen corrosion, the mechanism of which can be described according to the chemical reaction:
4Fe + 6H 2 O + 3O 2 = 4Fe(OH) 3 (1)
It is possible to distinguish standing corrosion from other types of corrosion by the presence of characteristic ulcers and the accumulation of corrosion products on the metal surface (Figure 1), formed under deposits of sludge, which contains a larger amount of moisture after boiler water is drained.
Figure 1 – Parking corrosion.
Methods for preserving drum steam boilers:
− dry shutdown of the boiler (SD);
− maintaining excess pressure in the boiler;
− filling the heating surfaces of the boiler with nitrogen (A);
− hydrazine treatment (HT) of heating surfaces at reduced boiler parameters;
− Trilon treatment (HT) of boiler heating surfaces;
− ammonium phosphate “boil down” (PV);
− filling the boiler heating surfaces with protective alkaline (PA) solutions;
− preservation of the boiler with a contact inhibitor (CI).
Methods for preserving once-through steam boilers:
− dry shutdown of the boiler;
− filling the heating surfaces of the boiler with nitrogen;
− hydrazine treatment of heating surfaces at boiler operating parameters;
− preservation of the boiler with a contact inhibitor.
The method of preservation of a steam boiler by dry shutdown is based on the principle of ensuring that the internal surface of the equipment is kept dry for the entire period of preservation. It is carried out by draining the boiler at a pressure above atmospheric (0.8 - 1.0 MPa), which allows drying internal surfaces drum, collectors and pipes due to the heat accumulated by the metal, lining and insulation of the boiler. To prevent moisture from entering, the 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; to do this, it is necessary from time to time to briefly open the drains at the lower points of the collectors and pipelines.
The preservation method by maintaining excess pressure 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 begin to fill it with conservation water and organize its flow through the boiler. A mandatory requirement for conservation water is the removal of dissolved oxygen in a deaerator. During the conservation period, the boiler is maintained at a pressure of 0.5 - 1.5 MPa and water flow at a speed of 10 - 30 m 3 / h. The oxygen content in the conservation water is monitored by monthly sampling from the clean and salt compartments of the superheater.
The preservation method by filling the heating surfaces of the boiler with nitrogen and maintaining excess pressure in the boiler prevents the access of oxygen and ensures the formation of a protective film on the metal surface. In case of boiler shutdown for a period of up to 10 days, preservation of the heating surface with nitrogen can be carried out without draining the boiler water. If shutdown requires a longer storage period, the water from the boiler must be drained. Nitrogen is supplied to the boiler through the superheater outlet manifolds and drum vents. During conservation, the gas pressure should be maintained at 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 stable when oxygen enters the boiler. The preparation of the preservative solution of reagents is carried out in a tank, the solution is supplied to the boiler using a dosing pump. The preparation of a preservative solution of the required concentration is carried out according to approved methods.
When choosing a preservation method for 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 must be carried out at least once a year.
2. A - filling the heating surfaces of the boiler with nitrogen.
3. Hydraulic fracturing + CO - hydrazine treatment at boiler operating parameters followed by dry shutdown; GO + ZShch, TO + ZShch, FV + ZShch - filling the boiler with an alkaline solution with previous reagent treatment.
4. TO + CI ( preservation with a contact inhibitor with previous Trilon treatment).
5. “before”, “after” - before and after repairs.
When preserving a once-through steam boiler, it is recommended:
1. In case of shutdown for up to 30 days, carry out conservation by dry shutdown of the boiler.
2. In case of putting the boiler into reserve for a period of up to 3 months or repair 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 case of longer periods of reserve or repair, preserve the boiler using a contact inhibitor or by filling the heating surfaces of the boiler with nitrogen.
Table 1 – Methods for preserving drum steam boilers
depending on the type and duration of downtime.
conclusions:
1. Preservation of a steam boiler during its downtime is carried out in order to prevent the development of standstill metal corrosion.
2. Methods for preventing parking corrosion are based on the principles:
– eliminating contact of air oxygen with the metal surface of the equipment;
– ensuring the metal surface is dry;
– creating a protective film on the surface of the metal or a corrosion-protective composition of water.
3. When choosing a method for mothballing steam boilers, it is necessary to take into account: the reason for putting the equipment into mothballing, the duration of the planned downtime of the equipment, design features equipment based on passport data.
4. Documentation for the conservation of a hazardous production facility is subject to an industrial safety review.
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 "Industrial safety rules for hazardous production facilities that use equipment operating under excess pressure." Approved by order of Rostechnadzor dated March 25, 2014 N 116.
