Eight common faults of deaerators and their solutions

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Eight common faults of deaerators and their solutions. 1. The role of the deaerator in the boiler system. As the name implies, a deaerator is used for removing oxygen; its function in the boiler system is to eliminate non-condensable gases and oxygen from the feedwater, thereby reducing the oxygen content in the feedwater and preventing oxygen-induced corrosion in the boiler system, thus ensuring the safe and stable operation of the boiler equipment. Additionally, the deaerator serves to collect water from various sources, recover working fluids, and reheat steam condensate. Various problems and abnormalities can occur during the operation of deaerators. For example, failures that lead to the shutdown of the deaerator, failure to use the associated deaerator, low deaeration efficiency of the deaerator, or fluctuations in management levels can all cause oxygen corrosion of the boiler itself as well as of the equipment and pipelines in the steam and condensate systems. This results in issues such as a red color in the boiler water and excessive iron content in the condensate. Oxide scale and corrosion beneath this scale may develop within the boiler system, leading to reduced boiler output and increased flue gas temperatures, which in turn wastes fuel and energy. If the boiler continues to operate under these faulty conditions for an extended period or if the problems are not properly addressed, it can lead to the escalation of accidents, causing the unit to stop operating, damage to equipment, and even safety incidents. II. Eight common faults of deaerators and their solutions. One of the eight common faults of deaerators and their solutions: High water level in the deaerator. There are usually 4 reasons for a high water level in the deaerator: 1 is an abnormality in the water level gauge ； 2 is a leak in the superheater system, with a large amount of drain water entering the deaerator ； 3 is failure of automatic water level adjustment ； 4 indicates a high water level in the series expansion tank, with water returning to the deaerator ； 5 is improper hydration. There are usually 7 methods to address high water level in the deaerator: 1 is to check and verify whether the water level gauge is functioning properly; if not, contact the thermal engineering team ； 2: When the water level in the deaerator rises rapidly, an immediate inspection should be carried out to reduce the water inflow rate to the deaerator ； 3: If the deaerator water level control valve fails automatically, it should be switched to manual mode for control, and the thermal engineering staff should be contacted to handle the issue ； 4 is the alarm when the deaerator water level is at high level I ； When the deaerator level reaches the High II value, the deaerator overflow valve is opened, the condensate recirculation system is activated, the drain from #3 high-pressure heater is closed, and the frequency converter of the condensate pump is set to its minimum flow rate. When the deaerator water level is at level III, the protection system shuts down the electric valves for the fourth-stage extraction steam as well as the extraction steam check valve; it opens the electric valve supplying auxiliary steam to the deaerator, and opens the drain valves before and after the fourth-stage extraction steam check valve. In the event of a protection shutdown, manually close the four-stage extraction steam electric valves and check valves ； 7 is when the high-pressure heater leaks; the high-pressure heater must be taken out of service ； 8 is to switch from continuous drainage to periodic drainage when the water level in the series expansion tank is high and backflow occurs into the deaerator. Eight common faults of deaerators and their solutions, Part 2: Low water level in the deaerator. There are usually 6 reasons for high water level in the deaerator: 1 is an abnormality in the water level gauge ； 2 is failure of automatic water level adjustment ； 3 is the incorrect closure of valves in the condensate water system or the incorrect opening of the recirculation system ； 4 is the accidental opening of the deaerator emergency drain valve ； 5 is condensed water or steam condensate, or a rupture or leakage in the feedwater pipes ； There are usually 9 methods for dealing with low deaerator water level as a result of condensate pump failures: 1 is to check and verify whether the water level gauge is functioning properly; if not, contact the thermal engineering team ； 2 is that when the water level in the deaerator drops rapidly, the inlet valve of the deaerator should be opened immediately to increase the amount of water flowing into it ； 3: If the water level control valve fails automatically, it should be switched to manual mode for adjustment ； 4 is to close the deaerator accident drain valve or condensate recirculation valve in case they open accidentally ； 5 is used to open the valve in the condensate water system when it closes accidentally ； 6 is to check for leaks in the condensate and feedwater systems; if any leaks are found, appropriate measures should be taken to seal them ； 7: If the condensate pump fails, it should be switched to the backup condensate pump for operation ； 8 indicates that when the water level is at level I, the amount of water added should be increased, and operation load should be reduced as appropriate ； When the water level is at low level II, efforts are made to increase the water supply; after 30 seconds, the feed pump trips automatically, and the unit should shut down due to a fault. Three of the eight common faults of deaerators and their solutions: An increase in deaerator pressure. There are usually 5 reasons for such an increase: 1 is an abnormality in the pressure gauge ； 2 is due to too low a water level in the deaerator and excessive steam inlet volume ； 3 is due to excessive unit load ； 4 means the #3 high-pressure heater is operating without water level ； 5. During startup, connect in series until the deaerator door opens. There are usually 7 methods to address an increase in deaerator pressure: 1 is to contact the thermal engineering team to verify that the instruments are accurate ； 2 indicates whether the steam inlet control valve of the deaerator is operating automatically properly; if automatic operation fails, it should be switched to manual mode ； 3: When the deaerator pressure is high, it is necessary to check whether the pressure of the fourth-stage extraction steam and the auxiliary steam are normal ； 4 is to check whether the high-pressure heater is operating without water level; adjust the water level control valve of #3 high-pressure heater in a timely manner to bring the high-pressure heater’s water level back to normal ； 5: In the event of a decrease in the water inflow to the deaerator, it is necessary to promptly check the operation of the condensate pump and adjust the water inflow to the deaerator ； 6: When the pressure in the series connection is too high, appropriately reduce the valve opening that leads from the series connection to the deaerator, so as to normalize the deaerator pressure ； 7: It is closed when the unit starts up and connected to the deaerator, and reopened after the unit is operating normally. Four of the eight common faults of deaerators and their solutions: Vibration in the deaerator itself and the connected pipes. There are usually 5 reasons for such vibration: 1 is improper heating during operation ； 2 is the entry of a large amount of cold water during deaerator operation ； 3 is due to too rapid pressure drop in the deaerator, resulting in vapor-liquid spouting ； 4 is the vibration of the deaerator caused by vibrations in the external pipes of the deaerator ； 5 refers to internal failures in the deaerator, such as the detachment of nozzles, which leads to steam-water impact and thus vibration. There are usually 6 methods for dealing with an increase in deaerator pressure: 1 is that if the deaerator vibrates, it is necessary to check whether the temperatures of the steam and water entering the deaerator, as well as the flow rate of the condensate, are appropriate, and make adjustments accordingly to eliminate the vibration in the deaerator ； When starting up the deaerator for heating, the water level should be maintained at 1/3 of its maximum level; the rate of temperature increase should be kept below 2°C per minute. The opening degree of the valve supplying auxiliary steam to the deaerator should not be too large, and care must be taken to ensure proper drainage from the pipes ； 2: When the deaerator temperature is high and the condensate water temperature is low, the flow rate should be reduced when feeding water ； 3 is to activate a backup steam source when the pressure drop in the deaerator occurs too rapidly, in order to reduce the rate of pressure drop in the deaerator ； 4 is to investigate the causes of vibration in the external pipes of the deaerator and take appropriate measures to eliminate such vibration ； When vibration is caused by full water level, check and close the make-up water valve and steam inlet valve on the deaerator, and open the drain valve to lower the water level ； 6: If the internal components of the deaerator are damaged, the output of the deaerator should be reduced to maintain stable steam pressure in it; shutdown may be necessary depending on the situation. Five of the eight common faults of deaerators and their solutions: High dissolved oxygen level in the deaerator effluent > 7 ppb. There are usually 6 reasons for high dissolved oxygen levels in the deaerator effluent: 1 is that inaccurate measurement values result from leaks or other issues with the sampling device ； 2 indicates a high oxygen content in the condensate water ； 3 is excessive condensate volume or too low condensate temperature ； 4 is due to the insufficient opening degree of the auxiliary steam supply valve to the deaerator at startup, resulting in inadequate heating of the deaerator ； 4 is due to the sticking of the check valve in the deaerator during its operation, preventing it from opening fully, which results in a reduction in the steam flow ； 5 is due to a blocked oxygen discharge pipe in the deaerator or an excessively small opening of the oxygen discharge valve ； 6 is the unit increasing load too quickly. There are usually 6 methods to address the high dissolved oxygen level in the water coming out of the deaerator: 1 is to check the accuracy of the measuring instruments using chemical tests ； 2 is to investigate the main reasons for high dissolved oxygen in the condensate water and take corrective action ； 3 is to check and ensure that each low-temperature heater is operating properly ； 4 is the control valve for regulating the auxiliary steam supply, ensuring stable steam supply for deaerator heating ； 5 is to check the status of the check valves and electric valves for the four-stage extraction steam supply to the deaerator, in order to ensure the deaerator operates under sliding pressure conditions ； 6 is used to adjust the opening degree of the oxygen discharge valve; if necessary, the start-up exhaust valve is opened to ensure unobstructed flow in the deoxygenation channel ； 7 is to appropriately reduce the load increase rate. Colleagues, what kind of failures have occurred with the deaerators of the steam boilers in your units, and how were they handled? Has there been any instance where the color of the boiler water or steam condensate was red or yellow, or where the iron content in the steam condensate was above the acceptable level? How did you solve it? What methods do you use for scale prevention and removal, as well as corrosion protection in boilers? Regarding issues such as adjusting the pH value of boiler feed water, redness of boiler water, hardness in return water, corrosion, scaling, and tube failures in boilers, corrosion in steam systems, excessive iron content in steam condensate, red color of acidic steam condensate, as well as testing and treatment of boiler water quality, Yan Hui from Beijing University of Chemical Technology at l86OO475386 is always available for industry colleagues to discuss these problems and exchange experiences. Students are also welcome to share information on new technologies related to boilers, while colleagues can share their experience in managing and using boiler equipment. Everyone involved in boiler operations is encouraged to learn from one another in order to solve various practical problems associated with boilers. Eight common faults of deaerators and their solutions. Sixth among the eight common faults of deaerators and their solutions: Overpressure in the deaerator. Overpressure can be indicated locally as well as on the display screen, with the deaerator pressure showing above the rated value; an alarm is triggered on the screen indicating high deaerator pressure, and the deaerator safety valve may activate. There are usually four main reasons for high dissolved oxygen levels in the water coming out of the deaerator: 1) The steam turbine is overloaded, resulting in excessively high pressure in the fourth stage of steam extraction ； 2 is due to improper adjustment of the deaerator feed water, resulting in a sudden decrease or even interruption in the feed water supply ； 3 is overpressure in the series expansion vessel with the safety valve failing to operate ； 4 is caused by the low water level in #3 high-pressure heater, which leads to steam flowing directly into the deaerator. There are usually 6 methods for dealing with overpressure in deaerators: 1 is to appropriately reduce the unit load ； 2 is to check whether the automatic level control of the condensate tank and deaerator is functioning properly; if necessary, switch to manual control to maintain a constant water supply volume to the deaerator ； 3 is to check whether the pressure in the series expansion tanks is normal; if overpressure in the series expansion tanks causes the safety valves to fail to operate, resulting in overpressure in the deaerator, quickly close the continuous blowdown valve of the steam drum and open the bypass valve for the series-to-settling water drain to relieve the pressure ； 4: If overpressure occurs in the deaerator due to steam being directly discharged into it as a result of the issue with #3 high-pressure heater, quickly close the normal drain valve of #3 high-pressure heater, investigate the cause of the low water level in the heater, and take appropriate actions ； 4: If the deaerator experiences overpressure due to poor automatic control, switch it to manual control. If water hammer occurs in the unit, it should be handled as a water hammer accident. 5: If the water level rises due to factors such as load, condensate flow rate, or temperature, its operating conditions should be adjusted to normal ； After shutdown, attention should be paid to the deaerator pressure to prevent it from operating under overload. Seven of the eight common faults of deaerators and their solutions: Low deaeration efficiency of the deaerator. Excess dissolved oxygen in water is the cause of this low deaeration efficiency. Usually, after the deaerator equipment in the boiler system is installed, there is not much change in its efficiency; however, under actual operating conditions, the deaeration efficiency of the deaerator tends to be low. To address the issues of low deoxidation efficiency in deoxidizers and excessive dissolved oxygen levels in water, six chemical agents are commonly used in conjunction with thermal deoxidation: sodium sulfite, hydrazine, propyl oxime, carbazide, acetaldoxime, ascorbic acid and its sodium salts. 1. Sodium sulfite is used to assist thermal deoxidation; the reaction equation between sodium sulfite and oxygen is: 2Na2SO3 + O2 → 2Na2SO4. Advantages of sodium sulfite for deoxidation: It can remove oxygen at room temperature ； Low investment, simple operation. Disadvantages of sodium sulfite for deoxidation: The dosage and frequency of addition need to be carefully controlled, as it is difficult to manage, and the deoxidization effect is unstable ； The salt content in the water in the boiler increases, which leads to higher waste discharge and greater heat loss ； Since sodium sulfite decomposes under high temperatures in boilers to produce harmful gases that cause metal corrosion, it is only suitable for medium and low-pressure boilers; it cannot be used in high-pressure boilers. It is generally employed in small boiler rooms and thermal systems with high requirements regarding water quality as an auxiliary deoxygenation method, and it is not appropriate for many applications where strict water quality standards apply ； Sodium sulfite is a strong reducing agent; it should be stored and used to prepare sodium sulfite solutions in sealed containers that are protected from contact with air, in order to prevent it from oxidizing and becoming ineffective. In practice, cases of sodium sulfite losing its effectiveness due to oxidation are quite common. The author has encountered several customers who continued to use nearly ineffective sodium sulfite for oxygen removal purposes. 2. It is heat-driven deoxidation assisted by hydrazine. Hydrazine is a strong reducing agent in alkaline aqueous solutions; it can reduce the dissolved oxygen in water, with the reaction equation being: N2H4 + O2 → N2 + 2H2O. Advantages of hydrazine for oxygen removal: Hydrazine does not increase the salt content in boiler water; the reaction it undergoes produces nitrogen and water, which helps to prevent further corrosion of the boiler. Disadvantages of hydrazine for oxygen removal: Hydrazine is a suspected carcinogen; it is volatile, toxic, and flammable. Safety precautions must be taken when using it, and it cannot be used in domestic boilers ； The excess amount of hydrazine should be appropriate; too much excess may carry unreacted hydrazine into the water vapor. 3. It is propyl oxime-assisted thermal deoxidation. Propanethioxime, abbreviated as DMKO or also known as dimethylthioxime, possesses strong reducing properties and readily reacts with oxygen in the feed water, thereby reducing the dissolved oxygen level in it ； Non-toxic, an ideal product for replacing traditional chemical deoxidizers such as hydrazine in feedwater for medium and high-pressure boilers. When in use, control the excess amount of propionoxime in the feed water at 15–40 μg/L. Advantages of propyl oxime for deoxygenation: non-toxic and causes no environmental pollution ； Propionoxime undergoes passivation reactions with metals, and can be used as a passivating agent after boiler pickling. Disadvantages of propionoxime for oxygen removal: It is a new type of oxygen remover, and further experience and methods for its use need to be developed and refined ； Some users have encountered tube failures due to corrosion of the boiler’s heating surfaces after using dimethyl oxime, and the cost is not low. 4. It is carbazide-assisted thermal deaeration. Carbazide, also known as diaminourea or carbamide hydrazide, has the molecular formula CON4H6. It is a derivative of dinitrogen; it is superior to hydrazine in terms of deoxygenation capabilities and metal purification. In the field of water treatment, carbazide can be used as a deoxygenating agent for boiler water, as well as a passivating agent for metal surfaces to reduce the rate of metal corrosion. Carbazide can react with dissolved oxygen in water to produce carbon dioxide, nitrogen, and water. The reaction between carbazide and oxygen is as follows: CON4H6 + 2O2 = 2N2 + 3H2O + CO2. The advantages of using carbazide for oxygen removal include its low toxicity, high melting point, and safe and environmentally friendly usage. Disadvantages of carbazide deoxygenation: It is generally used as an auxiliary thermal deoxygenation method, and it is expensive. 5. It is oxygen removal by acetaldoxime as an auxiliary to thermal oxygen removal. The molecular formula of acetaldoxime is C2H5NO. It is a reducing agent with low toxicity. In the 1990s, it replaced the highly toxic hydrazine as a deoxidizer for boiler water, and its deoxidization efficiency is 40 times that of hydrazine; as such, it is widely used in thermal power plants across the country as a new type of deoxidizer. By adding acetaldoxime to the unit using makeup water treated with chemicals, an excellent deoxygenation effect can be achieved. Especially when demineralized water is directly used as makeup water for the condenser, taking advantage of acetaldoxime’s ability to remove oxygen at low temperatures and at a rapid pace, most of the oxygen can be removed in the condenser, thereby reducing corrosion in the high-pressure heaters and their pipelines. Advantages of acetaldoxime for oxygen removal: It can remove oxygen at low temperatures, and the oxygen removal rate is fast ； Low toxicity. Disadvantage of acetaldoxime deoxygenation: The vapor mixed with air can be explosive ； Flammable hazard characteristic: easily ignitable; releases toxic nitrogen oxide gases when heated significantly ； Store away from sources of fire and heat; the storage temperature should not exceed 30°C, and it is expensive. 6. It is ascorbyl acid and its sodium salts used to assist in thermal deoxygenation. Isascorbic acid and its sodium salts are low-volatility deoxidizers; they are isomers of vitamin C (L-ascorbic acid). Their reaction with dissolved oxygen is complex, as it involves several intermediate steps to proceed, and the mechanism behind this process is not yet fully understood. Due to their safety, they are widely used as deoxidizers in food and feed applications. In our country, some manufacturers also use it as a deaerator for boiler water. Ascorbyl acid and its sodium salts are superior to hydrazine in terms of reducing iron ion levels and slowing down corrosion in the feedwater system; moreover, their final decomposition products are CO2, so they do not cause organic acid corrosion in the low-pressure cylinders of steam turbines. Advantages of ascorbyl acid and its sodium salts for deoxygenation: fast deoxygenation speed ； Non-toxic and safe. Disadvantages of ascorbyl acid and its sodium salts in oxygen removal: the need to control microbial growth in their dilute solutions ； Sodium erythorbate decomposes at high temperatures, producing corrosive dissolved solids; at 300°C, the decomposition products consist of 71.07% lactic acid, 20.48% acetate, and 8.44% formate. The sodium salts affect the conductivity of water and steam ； It can only remove oxygen without providing passivation. The eighth of the eight common faults of deaerators and their solutions: In situations such as excessive dissolved oxygen levels, low efficiency of the deaerator, shutdown due to deaerator failures, failure to use a complementary deaerator, not operating a deaerator, high operating costs for the deaerator, shutting down the deaerator, or when the deaerator is not suitable for the actual operating conditions, the BF-31T condensate protector, which offers good cost-effectiveness, excellent corrosion protection, and a low dosage per ton of feedwater, can fully replace the deaerator’s corrosion protection functions. The BF-31T condensate water system protector is a patented product of Beijing University of Chemical Technology, and it represents the core technology in the Science and Technology Ministry’s innovation fund project titled “Zero-waste steam generation technology”. This product passed the \"China Boiler Water Treatment Association Registration\" program in 2003. BF-31T condensate protector belongs to the category of chemicals added inside the boiler. It is not a traditional deoxygenation method that involves reacting with oxygen; instead, it uses a coating to isolate oxygen and carbon dioxide, thereby preventing corrosion throughout the boiler system and protecting the equipment and pipelines in the boiler system. This approach provides better corrosion protection compared to traditional deoxygenators. The BF-31T condensate system protector is a volatile alkaline agent; when added to the feedwater, it raises the pH levels of the feedwater, boiler water, steam, and condensate. It prevents weak acidic corrosion caused by CO2, can fully replace ammonia in its functions, and also addresses the issues associated with ammonia, such as its tendency to evaporate, the predominance of its vapor phase over liquid phase, the large amount required for use, and its inability to prevent oxygen-induced corrosion. The BF-31T condensate water system protector has an optimal gas-liquid ratio. Once added to the boiler system, it forms a monomolecular protective film on the metal surfaces in both the vapor phase and the liquid phase of the boiler water. This film not only possesses adsorption and hydrophobic properties but also does not affect the heat transfer efficiency of the boiler’s heating surfaces, tubes, and heat exchangers. The molecular spacing of this membrane is smaller than that of CO2 and O2, which prevents oxygen-induced corrosion as well as corrosion caused by weak acids resulting from CO2. This ensures that the concentration of iron ions in the steam condensate meets the requirements specified in the national standard GB1576-2008 \"Water Quality for Industrial Boilers.\" It eliminates the formation of iron ions at the source, protecting the equipment and pipelines in the boiler steam system and condensate recovery system. As a result, the equipment and pipelines in the entire boiler system are protected from corrosion, perforation, and leakage, eliminating potential hazards to the safe operation of the boiler system and extending the service life of the equipment. This approach truly addresses both the symptoms and root causes of the problem. The protective agent for the BF-31T condensate water system has excellent buffering capacity, unaffected by fluctuations in production load, and does not impact the performance parameters of water treatment ； The cost of the protective agents for the BF-31T condensate water system decreases as more of these agents are used within the system, and there are no issues related to wastewater discharge from backwashing or flushing processes involving other types of equipment. The BF-31T condensate system protector features a fast coating speed and high corrosion resistance; the iron ion level (total iron content) in the condensate water meets the specified standards within 72 hours, facilitating experiments to test the efficacy of this chemical. It can completely replace deaerators, deoxidizers, and high-temperature filtration iron-removal equipment. ▲Figure 1 shows that the boiler system is severely corroded, and the color of the steam condensate water is red. The BF-31T condensate water system protector deoxidation technology represents an upgraded version of traditional deoxidization methods; it isolates oxygen and CO2, thereby protecting all the equipment and pipelines in the boiler system. This approach not only prevents oxygen-induced corrosion but also avoids the mild acidic corrosion caused by CO2, achieving three benefits at once. Many users start by paying attention to, learning about, and trying out the BF-31T condensate system protector deoxidation technology, before eventually using it in practice. For example, a rail transit vehicle equipment company has 2 25-ton ultra-low nitrogen gas boilers, one in use and one as a backup, which are used to provide heating for drying purposes in the painting process. Due to the low workload of the new factory’s production lines, the boilers produce only a small amount of steam and operate intermittently; as a result, their operating conditions are not suitable for the proper functioning of the thermal deaerator, which therefore stops working. This causes the color of the steam condensate to turn red (see Figure 1). The high-temperature condensate, containing excessive iron, is discharged into sewers, leading to significant waste of energy and water resources. The boiler system suffers from severe corrosion. After trying the BF-31T condensate system protector, the iron content in the high-temperature steam condensate was reduced to acceptable levels, allowing it to be reused in the boilers. Corrosion was completely controlled, and the color of the condensate became clear and pure (see Figure 2). This approach achieved both iron removal and corrosion prevention, addressing the problem at its root while also helping to save energy and reduce emissions – achieving four benefits in one. ▲Figure 2: Condensate water sample from the condensation return water in the pilot test on the iron removal and corrosion prevention capabilities of the BF-31T condensate system protector. Advantages of the BF-31T condensate protector in terms of oxygen removal: particularly suitable for steam boilers ； Protecting the entire boiler system, its equipment, and pipelines not only prevents oxygen corrosion but also avoids the mild acidic corrosion caused by CO2 ； The iron ion content in the boiler water decreased significantly, while the iron ion content in the condensate quickly met the required standards; the effects were rapid and evident ； The service life of system equipment is extended, offering good overall performance and a high cost-performance ratio. Disadvantages of BF-31T condensate protector in terms of deoxygenation: It is non-toxic, but should be used with caution in boilers that have high requirements for steam quality, such as those where steam is used directly for cooking food or producing medicines. These are the eight common faults of deaerators and their corresponding solutions. In fact, there are many methods for deoxygenating boiler feed water. To remove oxygen and prevent corrosion in the boiler system, as well as to ensure the efficient, economical, stable, and safe operation of the boiler, it is necessary to take into account the type of boiler and the actual operating conditions of the user. Considerations such as the boiler’s thermal parameters, water quality, capacity, load variations, and economic factors should all be taken into account in order to select the most appropriate method for each situation. Eight common faults of deaerators and their solutions (Yan Hui)