Standby boiler

During the shutdown period of the boiler, oxygen and water vapor in the atmosphere continuously come into contact with various heating surfaces, causing oxidation and corrosion of the metal surfaces. Moreover, the degree of corrosion becomes more severe as the shutdown time prolongs and air humidity increases. Therefore, performing maintenance on the equipment (especially thermal equipment) during the shutdown period is a very important task. There are two methods for maintaining general thermal equipment: dry maintenance and wet maintenance. Dry maintenance and hot furnace water drainage maintenance: This is a maintenance method that utilizes the residual heat in the furnace after it has been shut down to dry out all the heating surfaces. It is generally suitable for boilers that need to be taken out of service for up to 7 days. The steps for this maintenance method are as follows: 1. After the boiler is shut down, drain the water from the furnace when the pressure in the steam drum drops to 5 bar ； 2. After all the water in the boiler’s tube banks has been drained, open some of the drum manholes ； 3. Open the drain valves of the drum and other tube banks, and ensure that all low-point drain valves are open. Verify that there is no moisture in the system and that ventilation is adequate, so that the entire boiler vessel remains dry. Desiccant maintenance: Desiccant maintenance is suitable for boilers that will be out of service for more than 30 days. The maintenance procedure is as follows: 1. Ensure that the boiler has been drained of water after being heated, so that no water remains inside the boiler ； 2. Place an appropriate amount of desiccant inside the drum; options for desiccants include quicklime, color-changing silica gel, alumina, etc ； 3. Seal the boiler to prevent water and steam from leaking into it ； 4. Open the drum manhole at least every 7 days to check for corrosion; replace the dried agent when necessary, and reseal the boiler after inspection. Wet maintenance: Wet maintenance refers to the use of chemical solutions (ammonia–hydrazine) to protect equipment, and it is suitable for maintaining boilers that have been shut down for 2 to 30 days. The basic maintenance procedures are as follows: 1. After shutting down the boiler, drain the water remaining in it, then fill it again with qualified deionized water, raising the water level to the maximum level indicated for the drum, to ensure that no water enters the superheater ； 2. Drain the solution from the phosphate dosing tank, clean it with deionized water, and prepare an ammonia-guanidine solution as required for protection in the dosing tank ； 3. An ammonia-hydrazine solution required for protection is also prepared in the ammonia and hydrazine dosing tanks ； 4. Add ammonia and hydrazine to the feed water tank and drum using ammonia solution, hydrazine, and phosphate dosing pumps ； 5. Circulate using the high and low pressure circulation pumps as well as the deaeration circulation pump for about 2 hours ； 6. After the cycle is completed, samples are taken from the feedwater and boiler water sampling points to analyze the pH and hydrazine levels in the water, with the pH to be controlled at approximately 12 and N2H4 at ≥200 ppm ； 7. Monitor the water levels in the feed water tank and drum; if they drop, add water and protective chemicals promptly ； 8. Take samples from the feedwater and boiler water sampling ports for analysis every other week or after water replenishment, and add chemicals as necessary. Octadecylamine maintenance: This is a method of protecting equipment by taking advantage of the chemical properties of octadecylamine as well as its highly volatile physical characteristics. Octadecylamine volatilizes into gases at high temperatures; these gases adhere to the inner walls of containers or pipes, forming a hydrophilic protective film that prevents water as well as oxygen or carbon dioxide in the atmosphere from coming into contact with the metal surfaces of the equipment, thereby protecting the equipment. The advantage of this maintenance method is that when the unit is restarted, as the temperature rises, the octadecylamine film decomposes rapidly into gases such as NH3 and H2, which can be easily expelled. Moreover, the gases resulting from the decomposition of octadecylamine that penetrate beneath the scale help to cause certain layers of scale to fall off, thereby reducing the rate of scale formation. The maintenance method is as follows: 1. Before adding chemicals to the system that requires maintenance, dilute the octadecylamine emulsion with deionized water first. 2. About 2 to 3 hours before the unit is shut down, the diluted chemical solution begins to be added to the system that requires maintenance (the location where the chemical is added can be determined based on the specific conditions on site; it is usually added at the pressure gauge connection at the inlet of the feed water pump). 3. During chemical dosing, samples of feedwater, condensate, boiler water, and steam must be taken for analysis until the concentration of octadecylamine meets the chemical requirements ； 4. Stop the machine 1.5 to 2 hours after adding the chemical, so that the solution can circulate fully and be distributed evenly ； 5. After shutting down, drain the water accumulated in the system that requires maintenance in accordance with the regulations for draining water while it is still hot.

See on page 2. Is \"protection by maintaining a slight positive pressure with nitrogen\" considered a method of protection?

Thank you for the valuable advice from the second floor. However, as long as our company ensures that nitrogen is continuously supplied inside the steam drum to maintain a slight positive pressure, the internal water vapor system should be able to remain isolated from oxygen. Would it be better to regularly light fires with wood in the furnace combustion area in order to remove moisture from the flue gas system? Thank you!

Advantages and disadvantages of 14 protection methods for shutting down boiler equipment. Boilers are devices for energy conversion; they represent high-value fixed assets and are the heart of industry. After the heating process is completed, it is very important to put the boiler equipment into shutdown and protection mode. Statistics show that corrosion of boiler equipment during periods of shutdown is more severe than during operation ； The vast majority of corrosion-induced perforations in boiler equipment occur not during operation, but during periods when the boilers are not in use. When boiler equipment is shut down and out of use, corrosion occurs mainly due to dissolved oxygen in the air or water. To prevent the metal inner surfaces of the boiler’s steam and water systems from being corroded by dissolved oxygen in the air or water, and to avoid an increase in electrochemical corrosion of the metal components in the boiler equipment and piping systems, it is important to adopt appropriate protective measures to ensure safety and extend the operational life of the boiler. The advantages and disadvantages of 14 different protection methods for shutting down and taking boilers out of service are generally categorized into three types: dry maintenance, semi-dry maintenance, and wet maintenance. One of the advantages and disadvantages of the 14 protection methods for shutting down and taking out of use boiler equipment – the nitrogen filling method. This method involves draining the water from the boiler after it is shut down, filling the boiler’s water system with nitrogen, and maintaining a certain positive pressure to prevent air from entering. Since nitrogen is highly inert and non-corrosive, it can prevent corrosion during boiler shutdown. The nitrogen filling method involves connecting the nitrogen supply pipeline before shutting down the furnace; once the pressure inside the furnace drops to 0.5 psig, nitrogen is supplied from nitrogen cylinders through temporary pipelines to areas such as the boiler drum and economizer. 4 requirements for the nitrogen filling method: 1. The purity of nitrogen should be over 99%. ⒉When filling the furnace with nitrogen with an empty furnace, the nitrogen pressure inside the furnace should be above 0.5 psig. ⒊When filling with nitrogen, all valves in the boiler water system should be closed, and it must be leak-free. ⒋During nitrogen protection, it is necessary to regularly check the pressure of nitrogen in the boiler water system as well as the airtightness of the boiler. If an excessive amount of nitrogen is consumed, the source of the leak should be identified and the leak fixed immediately. Disadvantages of the nitrogen filling method for shutting down and protecting the furnace: It is necessary to pay close attention to nitrogen leaks, conduct regular inspections on a daily basis, and address any issues that arise promptly. In practice, when using nitrogen inflation for long-term protection during boiler shutdowns, it is difficult to maintain a consistent level of nitrogen usage and pressure over an extended period; air often seeps in, causing the equipment to corrode and become unusable, necessitating its replacement. Therefore, the nitrogen inflation method is only suitable for protecting boilers that are shut down for short periods of time. Advantages and disadvantages of the second of the 14 protection methods for shutting down boiler equipment – drying method. The drying method involves, when a boiler is shut down, draining the water inside it once its temperature drops to 100–120°C; after the water has been completely drained, the residual heat in the boiler is utilized, along with a small flame or heated air introduced into the furnace, to dry the inner surfaces of the boiler. Disadvantages of shutdown and deactivation protection using the drying method: This method offers low protection efficiency and a short duration of protection, and is only suitable for temporary protection of boilers during maintenance. Third: Advantages and disadvantages of the coating method among the 14 protection methods for shutting down and taking out of use boiler equipment – The coating method involves draining water from the boiler equipment when it is shut down, removing contaminants, drying the metal surface of the boiler, and then applying a uniform layer of anti-corrosion coating on that surface to prevent corrosion during the period when the boiler is not in use. Anticorrosion coatings are generally made by mixing lead black powder with machine oil in a certain ratio. During application, it is required that all accessible areas be evenly coated. Disadvantages of the coating method for protecting boiler equipment when it is shut down: Although this method has good theoretical results and is suitable for long-term shutdown maintenance as well as for protecting equipment that remains idle for extended periods, it is difficult to implement in practice; it is not easy to apply coatings thoroughly in areas prone to corrosion such as bends, welds, and pipe walls ； Not only is the labor cost for applying it high, but the cost of activating the boiler equipment after protection is completed is also substantial; therefore, it is recommended to use this method with caution. Fourth: Advantages and disadvantages of the 14 protection methods for shutting down and taking out of use boiler equipment – Ammonia filling method. The ammonia filling method involves draining the water from the boiler after it is shut down and taken out of use, and then filling the entire volume of the boiler with ammonia gas. Ammonia dissolves in the water film on the metal surface, forming a corrosion-resistant protective layer on it. Ammonia can also reduce the solubility of oxygen in the water film, preventing corrosion by dissolved oxygen. Disadvantages of the ammonia filling method: Ammonia is corrosive, flammable, and explosive; its storage represents a safety hazard ； When using the ammonia filling method, copper components should be removed to prevent ammonia from corroding the components of copper-based equipment and to maintain the ammonia pressure inside the boiler. Fifth: Advantages and disadvantages of the desiccant method among the 14 protection methods for shutting down boiler equipment – The desiccant method involves, after the boiler is shut down, draining all the water from it once the temperature of the boiler water drops to 100–120°C. The residual heat in the boiler is then used to dry the metal surfaces, as well as to remove scale and sediment accumulated in the boiler’s water system. A desiccant is placed inside the boiler to keep the metal surfaces of the boiler equipment dry and prevent corrosion of the boiler system. Common desiccants include anhydrous calcium chloride (CaCl2), quicklime (CaO), silica gel, etc. Method of placing desiccants: Divide the drugs into several porcelain dishes and place them in different locations within the boiler; then immediately close all the steam valves to prevent outside air from entering the boiler. Disadvantages of using desiccants for shutdown and protection: Desiccants absorb moisture from the air inside the furnace; they only have a dehumidifying effect. After being placed in the furnace, they need to be checked regularly, and attention must be paid to any signs of deliquescence. If deliquescence is detected, the desiccant should be replaced immediately. Sixth: Advantages and disadvantages of 14 protection methods for shutting down boiler equipment – Dehumidifiers. Dehumidifiers are widely used abroad, and they provide effective protection when boilers are shut down. The main component of a dehumidifier is a rotating cylinder that turns 8 times per hour. A desiccant, lithium chloride (LiCI), is placed inside the cylinder. The cylinder is divided into two zones: the larger one serves as the surface for air to pass through, while the smaller one is used for the air undergoing regeneration. The treated dry air is blown into the boiler for maintenance work. After absorbing moisture, the desiccant in the cylinder is transferred to the regeneration zone, where heated regeneration air is introduced to drive out the moisture from the desiccant and restore its moisture-absorbing capacity. Then, the cylinder moves on to the processing area, and this process repeats continuously. Disadvantages of protection measures for shutting down dehumidifier and boiler equipment: Operating a dehumidifier on a boiler is complicated; it requires an air flow rate of 50 m3/h and a dehumidification capacity, and the cost of purchasing such equipment is high, in addition to the difficulties associated with its maintenance and repair. Seventh: Advantages and disadvantages of 14 protection methods for shutting down boiler equipment – TH-901, a protective agent for shut-down boilers. TH-901 is a scientific achievement developed by anti-corrosion experts at the Chemical Research Institute of the Ministry of Chemical Industry, as a solution to the shortcomings of traditional protection methods. It has been approved by the Boiler and Pressure Vessel Safety Assessment Committee of the Ministry of Labor. Principle of anti-corrosion protection by TH-90 boiler protection agent: TH-90 boiler protection agent is a solid powder that belongs to the category of gas-phase anti-corrosion agents. It is added to the equipment to be protected, and the equipment is sealed. The gas-phase anti-corrosion agent vaporizes, reaching a saturated vapor pressure similar to that in gas-liquid equilibrium; the vaporized components fill the gas space within the sealed container, forming a protective film with a thickness of one or several molecular layers on the metal surface. This prevents the metal surface from coming into contact with water, oxygen, or other corrosive gases, thereby suppressing electrochemical reactions and achieving anti-corrosion effects. Discontinuing the use of TH-901 as a boiler protector results in disadvantages when the boiler is shut down: excessive water accumulates inside the boiler, and the amount of chemical required also increases accordingly ； Not suitable for long-distance piping networks, nor for systems and equipment that lack appropriate openings to allow the placement of corrosion inhibitors ； It causes corrosion to the aluminum components and copper instrument parts on the boiler; isolation measures should be taken before using TH-901 to deactivate the boiler protector in order to prevent damage ； The acid-washed boiler should be passivated to prevent rusting, and then coated with TH-901, a protective agent for out-of-use boilers. 4 major advantages of TH-901, a boiler protection agent for shutting down boilers and protecting them during shutdown: 1. TH-901 provides highly effective corrosion prevention. After applying TH-901, a boiler protection agent, to idle or decommissioned steel equipment, there will be no signs of metal corrosion or rusting within one to two years (depending on the sealing condition of the equipment). ⒉TH-901 is easy to use as a boiler protector that does not require activation. When using TH-901 to deactivate boiler protectants, no drying equipment is required; after draining the water from the equipment that needs protection, the chemical can be added and the equipment sealed in one step, with no need for regular inspections. ⒊TH-901, a boiler protector that can be discontinued, has a wide range of applications. TH-901, a boiler protection agent that can be discontinued, is suitable for steel-based equipment and containers such as boilers, towers in chemical production facilities, reactors, tanks, pipes, drums, boiler drums, and header boxes. During the shutdown of the isomerization unit, the gas-phase anti-corrosion protection provided by sealing equipment TH-901 proved to be effective. ⒋TH-901, a boiler inhibitor that is no longer in use, belongs to the category of vapor-phase corrosion inhibitors; it requires a low dosage and offers good economic benefits. When reactivating equipment that uses TH-901 to deactivate boiler protectants and operates with water as the medium, there is no need to remove the unsublimated excess protectant; simply add water and start operation, which saves time, effort, and cost. The above introduced the 7 common dry protection methods used for shutting down and taking out of service domestic boiler equipment; below, the 7 common wet protection methods used for the same purpose will be discussed. Colleagues, what protection methods does your company use, and what is the effectiveness of those methods? Do you know of any successful cases of protecting boiler equipment from being shut down within or outside the industry? Regarding the protection methods, experiences, and issues related to the shutdown of boiler equipment, as well as issues concerning boiler water treatment – Yan Hui, Manager at Beijing University of Chemical Technology. Phone: I86OO47538. All colleagues and peers are welcome to come and discuss these topics at any time! We work together to solve problems and learn together about new technologies and methods for the anti-corrosion protection of boiler equipment during periods of long-term shutdown. Advantages and disadvantages of 14 protection methods for shutting down boiler equipment. Eighth: Advantages and disadvantages of 14 protection methods for shutting down boiler equipment – the alkali solution method. The alkali solution method involves adding alkali to fill the boiler with water having a pH level of over 10. It forms a corrosion-resistant protective film on the metal surface to prevent corrosion of the metal by dissolved oxygen. The alkali solution used is NaOH, Na3PO4, or a mixture of the two. Disadvantages of the alkali solution method for shutting down and protecting the boiler: It is necessary to maintain a uniform alkaline concentration in the solution, regularly monitor the boiler’s pH level, and be vigilant against the formation of secondary scale. Nine: Advantages and disadvantages of the 14 protection methods for shutting down boiler equipment – Sodium sulfite protection method. Sodium sulfite is a reducing agent that reacts with dissolved oxygen in water to form sodium sulfate, thereby preventing the metal surface from being corroded by dissolved oxygen. Additionally, a protective method using a mixed solution of trisodium phosphate and sodium sulfite can also be employed. This method is based on the fact that this mixture can form a protective film on the metal surface, thereby preventing the metal from corroding. Disadvantages of the sodium sulfite protection method for shutting down and taking the boiler out of service: When using this sodium sulfite wet protection method, the solution must be drained completely before starting the boiler, the boiler must be thoroughly cleaned, and then water and chemicals must be added again. Sodium sulfite is difficult to store, as it oxidizes and becomes ineffective very easily. In practice, it often happens that sodium sulfite that has already oxidized and lost its effectiveness is still being used; therefore, proper sealing and storage are essential when using sodium sulfite. Ten: Advantages and disadvantages of the thermal method among 14 protection methods for shutting down and taking out of use boiler equipment – The thermal method is used for shutdown periods of up to 10 days; it involves installing a water tank above the steam drum, which is connected to the steam drum via pipes. After the boiler is shut down, it is filled with water free of oxygen, and the water tank is mostly filled with water. The water tank is heated by external steam, keeping the water inside it in a constant state of boiling. Disadvantages of protection during shutdown by thermal method: The drawback of the thermal method is the need for an external steam source to supply steam. Eleven – Advantages and Disadvantages of 14 Protection Methods for Shutting Down Boiler Equipment: The Dimethyldithioxime Protection Method. Dimethyldithioxime is a commonly used chemical for the wet protection of boilers, serving as both a deoxidizer and a passivator. It not only possesses strong reducing properties but also exerts a passivating effect on metal surfaces. The method for using the dimethylthiosemicarbazone protection technique involves adding the pre-prepared dimethylthiosemicarbazone solution to the feed water tank; the concentration of this solution is determined based on the boiler’s volume, at around 300–400 mg/L. The pH value is adjusted to above 10.5 using ammonia (NH3), and after ensuring uniform circulation, the solution is fed into the superheater. After replenishing water and the chemical solution in the feed water tank, circulation is continued once more, after which the solution moves on to the reheater. Disadvantages of the dimethyloxime protection method for shutting down reactors: Dimethyloxime has a certain corrosive effect on copper; therefore, it is necessary to avoid any contact between the protective solution and copper or copper alloy components as much as possible ； The method for determining the concentration of dimethylthioxime is not yet perfect ； Dimethylthioxime has low toxicity. Advantages of the dimethyloxime protection method for shutting down reactors: Once a protective film forms on the metal, the pH level drops, but within a certain range, good protective effects are still maintained ； Dimethylhydroxime provides good protection for boilers during long periods of inactivity, and can replace the more toxic hydrazine ； Dimethyl homoxime waste is easy to treat. Restarting using the dimethylthioxime system performs well, and power plants have adopted the dimethylthioxime protection method in recent years. Twelve: Advantages and Disadvantages of 14 Protection Methods for Shutting Down Boiler Equipment – BF-30a Boiler Corrosion and Scale Inhibition Agent. With strong support from the Ministry of Science and Technology, Beijing University of Chemical Technology conducted systematic research on the issues of corrosion and scaling in boilers and heating systems. By applying the principle of \"synergistic action,\" it succeeded in developing the BF-30a boiler corrosion and scale inhibition agent, breaking away from the approach of treating boiler operation and shutdown separately; this agent solves both the problems of corrosion that occurs during boiler operation and those that arise when the boiler is shut down. This product features high efficiency, convenience, continuity, and low cost, bringing significant social and economic benefits. Protection mechanism of the anti-corrosion and scale-inhibition agent for BF-30a boilers against equipment shutdown: BF-30a provides a dual protection function by putting the metal of the boiler body into a passivated state and suppressing the cathodic reactions during metal corrosion, thereby effectively preventing oxygen corrosion as well as weak acidic corrosion caused by carbon dioxide, both during operation and when the boiler is shut down. Operation method for protecting BF-30a boiler anti-corrosion and scale-inhibition agent systems during boiler shutdown: Add the BF-30a boiler anti-corrosion and scale-inhibition agent to the boiler water; when the boiler is filled with water and the pH value of the boiler water reaches 12, seal the boiler. 8 major advantages of the BF-30a boiler corrosion and scale inhibition agent for protecting boiler equipment when it is shut down: 1. Technical specifications of the BF-30a boiler corrosion and scale inhibition agent: scale inhibition rate ≥ 99%, corrosion inhibition rate ≥ 99%, and corrosion inhibition rate during shutdown protection ≥ 99% – providing highly effective corrosion protection. After applying the BF-30a boiler corrosion and scale inhibition agent to idle equipment as well as deactivated steel equipment, a dense passivation protection film is formed on the inner metal surface of the boiler, preventing any signs of corrosion or rusting over one to two years. ⒉The anti-corrosion and scale-inhibition agent for BF-30a boilers is easy and convenient to use. Short dosing time ； When using the anti-corrosion and scale-inhibition agent for BF-30a boilers, no drying equipment is required, nor is it necessary to drain the boiler water; the agent can be added once and the equipment sealed, with no need for frequent regular inspections. ⒊The anti-corrosion and scale-inhibition agent for BF-30a boilers has a wide range of applications. The anti-corrosion and scale-inhibition agent for BF-30a boilers can be applied to steel containers such as boilers, towers in chemical production facilities, reactors, tanks, pipes, barrels, drum boilers, and header boxes. During the shutdown of the isomerization unit, using the anti-corrosion and scale-inhibiting agent for BF-30a boilers provides effective wet-method anti-corrosion protection. ⒋For boiler installations that use BF-30a anti-corrosion and scale-inhibition agents, equipment operating with water as the working medium can be restarted without any side effects; there is no need to remove the waste boiler water – water can simply be added and the equipment can be put back into operation, saving time, effort, and costs. The anti-corrosion and scale-inhibition agent for BF-30a boilers is suitable not only for providing anti-corrosion and corrosion-inhibition protection when boiler equipment is out of use for long periods, but also for such equipment that is shut down frequently for short periods – no additional treatment is required; simply shut down the boiler and seal it. ⒌The anti-corrosion and scale-inhibition agent for BF-30a boilers is an alkaline substance. BF-30a is used as a pH regulator; adding it to the boiler water raises the pH level of the water, thereby neutralizing and preventing the acidic corrosion caused by CO2 in the boiler water. ⒍The dispersant in the anti-corrosion and scale-inhibiting agent for BF-30a boilers can disperse iron scale, and when used as an iron scale dispersant, it can remove rust. ⒎The anti-corrosion and scale-inhibiting agent for BF-30a boilers exhibits a threshold effect: a non-stoichiometric low dose of the agent is used, meaning that the amount added is small. ⒏The anti-corrosion and scale-inhibiting agent for BF-30a boilers can chelate and remove old scale. The anti-corrosion and scale-inhibiting agent for BF-30a boilers possesses a strong chelating effect; when added to the boiler water, it forms stable water-soluble chelates with the hardness ions present in the water, thereby increasing the solubility of these ions. This helps to prevent the formation of scale, and it also has the effect of slowly dissolving existing scale. Thirteen – Advantages and Disadvantages of 14 Protection Methods for Shutting Down Boiler Equipment: The Ammonia-Hydrazine Protection Method. The procedure for this protection method involves draining the water remaining in the boiler drum after it is shut down, filling it with hydrazine, and using ammonia to adjust the pH value of the water, so that the concentration of hydrazine in the water remains above 200 mg/L, with the pH value ranging from 10 to 10.5. The ammonia-hydrazine protection method is suitable for protecting boilers that are out of use for long periods, in a cold standby state, or stored. During the protection period, it is necessary to regularly check the hydrazine concentration and pH value. 4 disadvantages of the ammonia-diammonia protection method for protecting boiler equipment during shutdown: 1. Numerous operating procedures. When restarting a boiler protected by the ammonia-hydrazine method, the hydrazine-ammonia solution should first be drained completely, and the boiler should be thoroughly rinsed. ⒉After the boiler is ignited, it is necessary to exhaust air first; steam can be supplied only when the ammonia content in the steam is less than 2 mg/kg, to prevent excessive ammonia concentrations from corroding the copper pipes. ⒊The hydrazine-ammonia protection solution is contaminated. The emitted hydrazine-ammonia protection solution must be treated before disposal to prevent pollution. ⒋A large amount of hydrazine is used. Since the temperature is at room temperature during protection using the hydrazine-ammonia method, the main role of hydrazine is not to react directly with oxygen to remove it, but rather to act as an anodic corrosion inhibitor or a sacrificial anode; therefore, an adequate amount of hydrazine must be used. On protection methods and experiences for shutting down boiler equipment. Beijing University of Chemical Technology, Yan Hui. I86OO47538. Welcome to all colleagues and students to communicate and discuss at any time! We work together to discuss solutions and learn about new technologies and methods for the anti-corrosion protection of boiler equipment during periods of long-term shutdown. Advantages and disadvantages of 14 protection methods for shutting down boiler equipment. Advantages and disadvantages of the 14 protection methods for shutting down boiler equipment – Fourteen to eighteen: the octadecylamine film-forming amine protection method. Mechanism of corrosion protection by octadecylamine film-forming amine: Octadecylamine film-forming amine is an organic long-chain compound containing nitrogen atoms; it has high surface activity. When in contact with a metal surface, its polar groups adsorb onto the active metal surface through chemical adsorption, while the lone pair of electrons on the nitrogen atoms forms covalent bonds with the empty orbitals of iron atoms. Its non-polar groups, on the other hand, adsorb onto the metal surface through physical adsorption. It can be seen that film-forming amines possess both anodic and cathodic corrosion inhibition effects on metals. Which specific inhibition mechanism plays a dominant role depends on various factors, among which temperature is of crucial importance. Under normal conditions, anodic corrosion inhibition plays a major role at high temperatures, while cathodic corrosion inhibition is dominant at low temperatures. Currently, some power plants are using octadecylamine for shutdown protection. The operation of the octadecylamine, or film-forming amine, method involves: during the process of shutting down the unit’s parameters, when the pressure in the steam drum drops to 10 MPa, injecting a solution containing film-forming amine into the boiler, so that this solution forms a protective layer within the water and steam system. To ensure thorough and uniform circulation of the chemical solution, the unit is brought to a smooth stop at a boiler water temperature of 240–304°C, after which it is allowed to stabilize for 1–2 hours. When the boiler pressure drops to 0.5 MPa, stop the boiler water pump from operating, and proceed strictly in accordance with the steps of draining water from the hot boiler and using residual heat for drying. At present, there are no unified standards for the implementation methods of octadecylamine, also known as film-forming amine; users can operate according to their specific requirements and circumstances, such as whether their boiler equipment is out of use or the unit is in standby mode. When using the octadecylamine, or film-forming amine, method for protecting boiler equipment during shutdown, 5 issues need to be taken into consideration: 1. Water and steam temperature. The film-forming effect of octadecylamine, also known as a film-forming amine, increases as the temperature rises, but once the temperature reaches a certain level, this film-forming effect decreases instead. 2. The concentration of the film-forming amine corrosion inhibitor is octadecylamine. Generally, the higher the concentration of octadecylamine, which is the film-forming amine corrosion inhibitor, the better the film-forming effect; however, when the concentration exceeds a certain level, the improvement in film-forming efficiency is minimal or even decreases. 3. Octadecylamine, or film-forming amine, exhibits good film-forming properties in the gas phase but poor properties in the liquid phase. 4. Roughness of the metal surface. The greater the roughness of the metal surface, the worse the film-forming effect. 5. Film formation time. A sufficient film-forming time is required to allow the octadecylamine, which acts as a film-forming corrosion inhibitor, to adsorb fully onto the metal surface; however, this time should not be too long to prevent a decline in the film-forming effect due to desorption. During periods of long-term shutdown of boiler equipment, effective anti-corrosion protection measures must be taken. When selecting a method for long-term shutdown protection, the goal should be the economic operation of the boiler. An appropriate protection method should be chosen based on the structure of the boiler equipment to be taken out of service, the duration of shutdown, the quality of water, the characteristics and effectiveness of various anti-corrosion protection methods, as well as the actual operating conditions and economic costs of the facility in question. Advantages and Disadvantages of 14 Protection Methods for Shutting Down Boiler Equipment (Yan Hui)