deaerator

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I. Overview: When condensate flows through a negative-pressure system, air can leak into the condensate from areas where the seals are not tight. In addition, there is also a certain amount of air present in the make-up water. Under certain conditions, this air not only corrodes the equipment in the system but also reduces the heat exchange efficiency of heaters and boilers, thereby decreasing the economic efficiency of the unit. To reduce corrosion in the feedwater system, as well as in the economizers and water wall tubes, the main approaches are to reduce the dissolved oxygen in the feedwater, or to increase it appropriately under certain conditions in order to mitigate oxygen corrosion; additionally, raising the pH value of the feedwater helps to prevent CO2-induced corrosion. Deoxygenation methods are divided into chemical deoxygenation and thermal deoxygenation. Power plants generally use thermal deoxygenation as the main method, with chemical deoxygenation used as a supplementary approach. In chemical deoxygenation, certain chemicals that readily react chemically with oxygen are used to react with the oxygen dissolved in water, producing substances that do not cause corrosion to metals, thereby achieving deoxygenation. Chemical deoxygenation can only completely remove oxygen from water, but not other gases; moreover, the oxides formed increase the content of soluble salts in the water. Additionally, the chemicals used are expensive, so chemical deoxygenation is used only as an auxiliary method for removing oxygen. A deaerator is a mixed-type heater that operates on the principle of thermal deaeration, capable of removing dissolved gases from feedwater ； It can also store a certain amount of feedwater, thereby alleviating the imbalance between the flow rates of condensate water and feedwater ； Reheat steam extraction can also be used to heat the feedwater, thereby improving the thermal efficiency of the unit. In thermal system design, deaerators are also used to recover high-quality condensate and steam leaks from valve stems. During normal operation of the unit, a combined water treatment method involving ammonia addition and oxygen addition is employed (i.e., the CWT mode); in this case, the deaerator performs the function of a heater while also removing other water-soluble gases ； During the startup phase or in cases of abnormal water quality, ammonia or hydrazine is added to the feed water (i.e., under the AVT condition) to reduce the oxygen content in the water and thereby slow down oxygen corrosion; at this time, the deaerator serves both to heat the feed water and to remove oxygen from it. The design of the deaerator must meet the following requirements: it should have a deaeration capacity sufficient to meet the boiler’s maximum load, have a large enough water volume with some margin, and include measures to prevent overpressure and excessive water levels. The design of the heating steam source for the deaerator is determined by the operating mode of the deaerator system. When the deaerator operates primarily to meet the basic load, it is usually run at a constant pressure. A pressure control valve is installed on the steam supply pipeline; the pressure of the steam source is required to be slightly higher than the constant-pressure operating value, and a steam source with an even higher pressure is provided as a backup. This method results in high throttling losses and lower efficiency. In deaerators that primarily use sliding pressure operation, no control valves are installed on the steam supply lines, and the pressure in the deaerator changes according to the load of the turbine set. This mode of operation is more efficient as there is no throttling. II. Working Principle of the Deaerator 1. The thermal deaeration principle is based on Dalton’s law and Henry’s law as its theoretical foundations. 1.1 Henry’s law states that at a constant temperature, when a gas dissolved in water is in equilibrium with other substances present in the water, the amount of gas dissolved per unit volume of water is directly proportional to the partial pressure of that gas above the water surface. The partial pressure of a gas at equilibrium is called the equilibrium pressure. If the partial pressure of a gas at the water surface is lower than the equilibrium pressure corresponding to the gases dissolved in the water, that gas will separate from the water under the effect of this pressure difference until a new equilibrium is reached. If the gas can be completely removed from the water surface, bringing its actual partial pressure to zero, then the gas can be entirely eliminated from the water. This is the basic principle of thermal deoxidation. 1.2 According to Dalton’s law, the total pressure of a gas mixture is equal to the sum of the partial pressures of its constituent gases. In the deaerator, the amount of steam above the water surface keeps increasing, and the partial pressure of the steam gradually rises; by removing gases promptly, the partial pressures of various gases above the water surface decrease accordingly. When water is heated to its saturation temperature at the pressure of the deaerator, a large amount of water evaporates, and the partial pressure of water vapor approaches the total pressure above the water surface. As gas is continuously removed, the partial pressures of various gases above the water surface tend to zero, allowing the gases present in the water to escape and be removed. 1.3 Thermal deoxidation is a process of heat and mass transfer; to achieve optimal deoxidation results, the following conditions must be met: (1) The water must be heated to its saturated temperature at the pressure in the deoxidizer, so that the pressure of water vapor above the water surface is close to the total pressure at that surface ； (2) The gases escaping from the water must be removed promptly, so as to reduce the partial pressures of various gases on the water surface to zero or a minimum ； (3) The deoxygenated water and the heating steam should have sufficient contact area, and they should flow in opposite directions; this not only enhances heat transfer but also ensures a large pressure difference, thereby enabling the gas to be separated. 2. The process of gas separation from water can basically be divided into two stages: the first stage is the initial deoxygenation stage. At this time, due to the high amount of gas in the water, the pressure difference is large; the gas escapes in the form of small bubbles, overcoming the viscosity and surface tension of the water. At this stage, 80%–90% of the gases in the water can be removed. The second stage is the deep deoxygenation stage. At this point, since there is still a small amount of gas remaining in the water, the resulting unbalanced pressure difference is very small; the gas no longer has enough energy to overcome the viscosity and surface tension of the water in order to escape, and it can only gradually separate through the diffusion of individual molecules. At this point, increasing the surface area of contact between the soda and water can help form a water film, reducing its surface tension and thus allowing the gas to diffuse more easily. The bubbling of steam in water can also be used to cause gas molecules to attach to the bubbles and escape from the water. III. Introduction to Deaerators 1. Structure of Deaerators The main components of a deaerator include the shell, supports, water inlet device, spring nozzles, water receiving tank device, water dispersing bucket device, deaeration tray, internal platform, steam exhaust device, heating steam device, high-pressure heater drain device, recirculation pipes, and reboiling device, among others. 1.1 The shell is formed by welding a cylinder body with two standard elliptical end caps; it is placed in a horizontal position, and the material used is 16MnR ； The shell is welded with external connection pipes of different specifications, used for connecting various types of steam and water to and from the deaerator. Each of the end caps is equipped with a DN600 manhole for installation and maintenance purposes. The 1.2-stage deaerator has three saddle-type supports, which are installed at the bottom of the deaerator; the middle support is a fixed support while the two end supports are sliding supports, allowing the deaerator to slide freely as it expands due to heat. 1.3 The water inlet device is fabricated by welding a Φ480×14 feed main pipe with 16 Φ108×9 pipe fittings evenly distributed along the entire length of the main pipe. The condensate is distributed to various connections through the feed main, and then flows into the spring nozzles. 1.4 The spring-nozzle deaerator is equipped with 16 nozzles, each with a capacity of 100 t/h, evenly distributed across its top. The nozzle and the water inlet device are connected by welding. The nozzle component is made of stainless steel. The pressure difference at the rated flow rate (100 t/h) for the nozzle is around 0.05 MPa, and the flow rate of the nozzle increases as the pressure difference increases. The nozzle is adjusted using springs to ensure proper water film formation under various load conditions, thereby meeting the requirements of deoxygenation equipment operating under changing conditions. At the same time, the nozzle also acts as a check valve, preventing steam from flowing back into the condensate water; thus, this nozzle helps to prevent water hammer effects, and it is often referred to as a spray valve. The condensate is distributed through the feed main pipes to various spray valves, which emit water in a film form; this water comes into contact with the heated steam rising from the bottom of the deaeration tray, and is heated to or near the saturation temperature at the operating pressure of the deaerator. 1.5 Water receiving tank assembly (deaerator internals): The water receiving tank is made by pressing stainless steel sheets, and it is fixed to the side plates as well as the front and rear partitions using bolts and nuts. Its function is to collect the water sprayed by the spray valves, direct it in the specified direction, and distribute it to the distribution buckets located below the water receiving tank. 1.6 Sprinkler bucket assembly (deaerator internals): The sprinkler bucket assembly is a bucket-shaped structure made of thin stainless steel plates, which are fixed to the baffle using bolts and nuts. It is used to collect water distributed by the water distribution tank. A set of such sprinkler bucket assemblies has 300 holes with a diameter of Φ14.5 at their bottom, allowing water to fall evenly in the form of fine streams onto the serrated surfaces below; this causes the water to be fragmented and broken up before falling like rain onto the deaeration tray beneath. 1.7 Deoxidation tray device (deoxidizer internal component): The deoxidation tray is an efficient deoxidization element; this equipment is equipped with 128 such trays, made of SA-240TP and 316L materials. Each deoxygenation tray is composed of V-shaped strips made by pressing together several stainless steel strips; each V-shaped strip has many smooth, serrated grooves on its edges, where the water is further broken down and fragmented, forming layers of film that flow downward. At the same time, the water also moves laterally within the deoxygenation tray. The deoxygenation plates are fixed within a frame made of angle steel; the connection between each pair of plates is achieved by fitting them together using notches. After the last deoxygenation plate is installed, it should be secured in place using adjustment plates, according to the actual conditions. The specific assembly of these adjustment plates is outlined in the assembly diagram (F0032560010751). 1.8 The internal platform is equipped with three small platforms and three escalators inside the deaerator; these are used for assembling the deaeration tray after the on-site hydrostatic test is completed, and can also be used for maintaining other internal components. 1.9 Exhaust System: The exhaust system of this deaeration equipment is divided into startup exhaust and continuous operation exhaust. One Φ108×4 start-up vent pipe is provided in each of the left and right sections of the equipment, and an electric exhaust valve and a pressure reducing valve are installed on these pipes to facilitate the efficient removal of non-condensable gases and oxygen from within the equipment during startup. The continuous operation exhaust device consists of 16 steam extraction pipes evenly distributed across the equipment, along with throttle orifice plates on these pipes. While the equipment is operating continuously, 16 steam extraction tubes and throttle orifices are used to continuously remove oxygen and other non-condensable gases, ensuring that the oxygen and other non-condensable gases generated during the deoxygenation process are removed promptly. 1.10 Steam heating device: The steam heating device consists of pipes with dimensions Φ480×14, sleeves, and an anti-erosion device; the anti-erosion device is used to prevent steam from eroding the vessel walls and internal components once it enters the chamber. The casing is used to prevent high-temperature steam from coming into direct contact with the cylinder wall, thereby avoiding excessive local temperature difference stresses. 1.11 Superheater Drain Device: The superheater drain device consists of a pipe with dimensions Φ426×11 and mounting fixtures; it features 20 oval holes measuring 40×240 on its surface, which allow the drain fluid from the superheater to flow smoothly into the deaerator for flashing. Tube material: For the feed water pump recirculation pipes and recirculation connections, there are a total of 3 tubes; 2 of them have a diameter of Φ273×11, while the third one has a diameter of Φ219×9. These tubes are inserted below the normal liquid level in the water tank, and each of them has 232 holes with a diameter of Φ18. One of its functions is to return the feedwater to the deaerator through the recirculation pipe during unit startup or at low load, thereby maintaining the flow rate of the feedwater pump and preventing cavitation and vibration in the feedwater pump ； Secondly, when the unit starts up, the oxygen content in the feed water does not meet the standards, preventing water from being supplied to the boiler; as a result, the deoxygenated water is returned to the deaerator through the recirculation pipe. 1.13 The deaerator of the reboiling unit is equipped with two externally connected reboiling nozzles. The reboiling unit consists of two inlet pipes with a diameter of Φ273×7, a steam distribution main pipe of the same diameter, and 18 evenly distributed branch pipes. Steam is ejected through 12 Φ10 small holes on each branch pipe, allowing the water to be heated evenly; this design helps to reduce vibration and noise. The function of the reboiling device is, first, to heat the cold water as quickly as possible to the saturation temperature at the operating pressure of the deaeration equipment during unit startup, thereby accelerating the deoxygenation of the feedwater; second, in normal operation, if the oxygen content in the feedwater is not within the specified limits, auxiliary steam can be introduced through this pipe to cause the water in the deaerator to reboil, thus assisting in the removal of oxygen and other non-condensable gases from the feedwater. 2. In the deaeration process of this deaerator, the condensate enters the spring nozzles through the feed water main. Since the pressure of the condensate is higher than the operating pressure inside the deaerator, the pressure difference causes the nozzles to open, and the condensate is sprayed in a film form into the first and second receiver tanks. The water stored in these receiver tanks is fragmented and broken as it passes over the serrations on the dispersal buckets below, before flowing evenly onto the deaeration tray beneath. During this process, steam flows upward from below, coming into full contact with the condensate and heating it to a temperature close to the saturation temperature at the deaerator’s operating pressure, thereby removing most of the oxygen from the condensate. The heated and deoxygenated condensate water is evenly spread over the deoxygenation tray below; there it is continuously broken down and fragmented, forming layers that flow downward in a film-like manner. At the same time, the water also moves laterally within the deoxygenation tray, increasing the surface area for contact between water and steam. This ensures sufficient time for mass and heat transfer, allowing the condensate water to come into full contact with the steam rising from below, thereby providing enough time and momentum for dissolved oxygen to escape. Thereby achieving deep deoxygenation, so that the oxygen content in the boiler feedwater meets the specified standard values. The oxygen and other non-condensable gases that are continuously released during the deoxygenation process are discharged continuously through the 16 steam exhaust pipes at the top, via throttle plates and steam exhaust headers. Deoxygenated water that meets the standard values is stored in the lower water storage area to meet the requirements for boiler feed water. 3. When the deaerator is operating properly, its water storage capacity is sufficient to sustain operation at BMCR conditions for 5 to 10 minutes ； The water storage capacity of our company’s water tank corresponds to the water supply consumption over 6.5 minutes at the boiler’s maximum continuous evaporation rate (BMCR). The water storage capacity of a tank refers to the amount of water stored between the normal water level in the tank and the water level at the top of the tank’s outlet pipe. Under normal operating conditions (sliding pressure operation), the oxygen content at the outlet of the deaerator is ≤5PPb (μg/l). When the boiler is started at cold conditions, the deaerator can operate at the specified pressure and flow rate, and the water temperature meets the requirements for boiler startup. In abnormal operating conditions such as the shutdown of the low-pressure heater, the deaerator is capable of meeting the requirements for feedwater temperature and flow rate under such circumstances. The deaerator has high efficiency, enabling steam discharge losses to be reduced to a minimum. 4. Safety protection system 4.1 To prevent overpressure in the deaerator, two A48Y-25 spring-loaded full-opening safety valves are installed; their operating pressure is 1.4 MPa. The total steam discharge capacity of these two safety valves is approximately 126.876 t/h. When the operating pressure inside the deoxidation equipment reaches 1.4 MPa(g), the safety valve opens automatically to release pressure, thereby providing safety protection. 4.2 Overflow and emergency drain pipes: Excessively high water level in the deaerator can lead to overpressure in it; when the water level in the deaerator gets out of control or even reaches its maximum level, it can cause water to enter the turbine, resulting in serious accidents. Therefore, the deaerator is equipped with a deaerator overflow and drain port, and a high-water-level limit is included in the sequential control (see figure below). Both water discharge outlets are above the normal water level. When the water level in the deaerator or emergency drain pipe rises to a high level, the overflow valve is opened first to release some of the feedwater ； When the deaerator level rises to a high-high value, the emergency drain valve opens. Both circuits are drained to the condenser. 4.3 Shutdown drain pipe: When the deaerator needs to be drained while it is shut down, the lowest-mounted shutdown drain valve can be opened to drain water into the pressurized drain header. 5. Steam supply method for the deaerator: The operating mode of this equipment is fixed-pressure, sliding-pressure, then fixed-pressure operation. The deaerator operates at a constant pressure using auxiliary steam during startup ； Once the unit reaches a certain load, the heating steam is switched to the reheat cold section, and then to the fourth-stage extraction steam of the turbine, allowing for sliding pressure operation ； Once the unit load drops to a certain level and the fourth stage of steam extraction is no longer sufficient to meet the requirements of the deaerator, operation is switched back to the reheat cold section or auxiliary steam, allowing operation at constant pressure. During sliding pressure operation, its pressure varies according to the load of the unit. The extraction pipeline is equipped only with an electric shut-off valve and a check valve to prevent water and steam from entering the turbine, with no control valves installed. The sliding pressure operation range is: 0.147MPa–1.314MPa (a); for auxiliary steam, the pressure is 0.8MPa and the temperature is 250°C℃ ； Deionized water: pressure 3.0 MPa, temperature ~20 ℃. 6. Deaerator measurement devices: 1) The deaerator is equipped with 3 sets of single-chamber balance vessels, installed on both sides of the deaerator. Use it to obtain the high and low water level signals of the deaerator. When the water level in the deaerator is above or below the normal level by a certain amount, the water level signal generated by the balance tank is converted into an electrical signal via a pressure difference transmitter and sent to the automatic water level control device for adjustment. 2) 2 sets of magnetic flap level gauges, one set installed on each side of the deaerator, to monitor the water level inside the deaerator in real time. 3) Two pressure gauges are installed on the left and right sides of the deaerator to monitor the pressure inside the vessel in situ. 4) Two bimetallic thermometers are installed on the left and right sides of the deaerator to monitor the temperature of the medium inside the deaerator in real time. 7. The deaerator is arranged to prevent cavitation in the feed water pump; the feed water pre-pump is located at zero meters, while the deaerator is situated at 24.0 meters, thereby increasing the effective net positive suction head of the feed water pump. 8. Deaerator water level protection 8.1 The high water level protection for the deaerator is divided into three levels: Level 1 – High water level: Alarm (the operator opens the overflow valve if it is deemed necessary) ； Second stage – high water level: Open the emergency discharge valves for urgent water release ； Third stage – high dangerous water level: Forcefully close the extraction check valve and the extraction electric valve. When the water level reaches the normal value, the emergency discharge gates and overflow discharge gates can be closed. 8.2 The low water level protection for the deaerator should be divided into two levels: the setting diagram for the deaerator water level protection is shown below. First stage – low water level: alarm ； Second stage – low dangerous water level: shut down protective devices such as feed water pumps. IV. Technical Specifications for the Deaerator
1. Structural Parameters of the Deaerator
Table of Deaerator Structure Types:
| Serial No. | Parameter | Value |
|-------------|-----------|-------|
| 1 | Deaerator type | Horizontal, headless, spray-type |
| 2 | Deaerator model | SSD-2010/235 |
| 3 | Total volume of deaerator | 357 m³ |
| 4 | Effective volume of deaerator | 235 m³ |
| 5 | Maximum output of deaerator | 2010 t/h |
| 6 | Inner diameter | 3800 mm |
| 7 | Length | 32668 mm |
| 8 | Wall thickness | 28 mm |
| 9 | Net weight | 124215 kg |

2. Technical Parameters of the Deaerator
Table of Deaerator Technical Parameters:
| Serial No. | Parameter | Value |
|-------------|-----------|-------|
| 1 | Design pressure | 1.48 MPa |
| 2 | Design temperature | 381°C |
| 3 | Maximum operating pressure | 1.314 MPa (a) |
| 4 | Maximum operating temperature | 400.5°C |
| 5 | Rated output per nozzle | 100 t/h |
| 6 | Setting pressure of safety valve | 1.4 MPa |
| 7 | Flow rate of safety valve | 126.876 t/h |
| 8 | Oxygen content in outlet condensate | ≤ 5 μg/l |
| 9 | Temperature of condensate at inlet | 140.8°C |
| 10 | Temperature of condensate at outlet | 187.9°C |

3. Water Quality Requirements
Table of Requirements for Feedwater Quality to the Deaerator:
| Serial No. | Parameter | Value |
|-------------|-----------|-------|
| 1 | Cation conductivity (25°C) | ≤ 0.15 μS/cm |
| 2 | pH value | 8–9 |
| 3 | Hardness | ≈ 0 mmol |
| 4 | Iron ions (Fe) | ≤ 10 μg/l |
| 5 | Copper ions (Cu) | ≤ 3 μg/l |
| 6 | SiO2 | ≤ 15 μg/l |
| 7 | Dissolved oxygen | 30–200 μg/l |

V. Operation of the Deaerator
1. Overview
1.1 During the start-up and shutdown of the unit, when the load is less than 15% of BMCR, the deaerator operates at a constant pressure, with the pressure being maintained at 0.147 MPa using auxiliary steam. 1.2 When the four-extraction pressure meets the requirements, it switches to using steam from the deaerator as the source of steam, entering the variable-pressure operation phase. 1.3 During normal operation, the four-stage extraction steam from the main turbine is used to maintain a sliding pressure operation mode for the deaerator, with the sliding pressure range being 0.147 MPa to 1.314 MPa. 1.4 In the event of an accident or shutdown, when the load drops to 20% of BMCR, the steam supply is switched from the fourth extraction stage to make-up steam, allowing operation at a constant pressure of 0.147 MPa. 1.5 The regulation of the deaerator water level is primarily achieved through two deaerator feed control valves (equipped with electric bypasses), and there are also water level interlock and protection devices in place. 2. Startup of the deaerator 2.1 Pre-startup checks and preparations (1) Check and confirm that the condensate water system is operating properly, that the quality of the condensate water is satisfactory, and that the pressure and temperature of the auxiliary steam meet the required standards. Ensure that the water level transmitter and the local water level gauge of the deaerator are functioning correctly, and that the water level interlock protection system has been tested successfully. (2) Check and close all the following valves: drain valve, feedwater pre-pump inlet valve, high-pressure heater exhaust valve, nitrogen filling valve, high-pressure heater drain valve, electric isolation valve from the fourth extraction unit to the deaerator, electric isolation valve from the auxiliary steam to the deaerator, as well as the water level control valves and bypass valves for both deaulators ； (3) Check and open the following valves: the manual valves before and after the water regulation valves on the two deaerators, the manual valves of the electric valves used to supply auxiliary steam to the deaerators, the manual valve of the electric valve for draining water from the deaerator, the start-up drain valve of the deaerator, and the continuous drain valve. (4) Warm up the auxiliary steam and fourth extraction steam supply pipes, and drain water. 2.2 Water feeding for heating: Water feeding to the deaerator begins only after the condensate system has been successfully flushed. The deaerator flushing can be carried out simultaneously with the feedwater system flushing; flushing is considered successful when the iron content in the feedwater at the deaerator outlet is ≤50 μg/l and the suspended solids content is ≤10 μg/l. Open the feed water control valve for the deaerator to supply water to it until the normal water level is reached; then set the valve to automatic mode, so that it can maintain the water level in the deaerator at the set value. After the water supply is complete, slowly open the steam supply control valve for the make-up steam to the deaerator, so that the temperature and pressure of the deaerator increase. During the heating process of the deaerator, pay attention to controlling the rate of temperature and pressure increase to prevent vibration in the deaerator. The temperature rise rate is kept at around 30–40°C per hour, and the pressure increase rate is less than 2 Kpa/min, so as to heat the water temperature in the deaerator to meet the requirements of the boiler for the feedwater temperature. When the pressure in the deaerator approaches 0.147 MPa, the pressure control valve of the deaerator is switched to automatic mode, and it automatically maintains a constant pressure in the deaerator. When the water temperature in the deaerator reaches 111°C, the start-up exhaust valve of the deaerator can be closed based on the oxygen content in the feedwater, and the opening degree of the continuous exhaust valve can be adjusted to reduce steam and water losses. When water is added to the boiler, the amount of water processed by the deaerator increases; at this time, special attention should be paid to the vibration of the deaerator, and the water inflow rate should not increase suddenly by too much. 3. Operation of the deaerator 3.1 Switching of the steam source for the deaerator: When the pressure in the fourth extraction line is higher than that in the deaerator, the electric isolation valve for the fourth extraction line is opened to maintain a pressure slightly above 0.147 MPa; thereby the steam source for the deaerator is switched to the fourth extraction line. After the auxiliary steam source is taken out of service, the drain valve on the steam supply pipe should be opened to keep the auxiliary steam supply pipeline in a hot standby state. Once the switching is complete, the deaerator enters the variable pressure operation mode. When the unit load exceeds 20%, after the electric isolation valve for the fourth extraction steam supply to the deaerator is opened, it is necessary to ensure that the drain valve on the fourth extraction pipeline is closed. 3.2 Oxygen return and regenerative boiling in deaerators: Whether operating at a constant pressure or under variable pressure, deaerators may experience oxygen return or regenerative boiling when the load changes, with this phenomenon being more likely to occur in deaerators operating under variable pressure. As the load increases, the pressure inside the deaerator rises as well. However, the water temperature in the deaerator changes more slowly than the pressure, and it does not rise immediately, resulting in sub-saturated water. Since the solubility of gas in unsaturated water is greater than that in saturated water, the gas that has already precipitated returns to the feed water, reducing the deoxygenation efficiency; this is known as the \"re-oxygenation\" phenomenon. “The occurrence of the “oxygen return” phenomenon does not cause cavitation in the feed water pump. During operation, a sudden increase in pressure in the deaerator is unlikely, while a sudden drop in pressure occurs frequently, which can lead to the phenomenon of \"reboiling\" in the deaerator. The mechanism of reboiling in a deaerator lies in the fact that the saturation temperature of water varies with pressure, with higher pressures corresponding to higher saturation temperatures. When the pressure in the deaerator drops suddenly, the feedwater temperature is higher than the saturated temperature of the feedwater at that pressure, causing the feedwater to vaporize, a phenomenon known as \"reboiling\". Based on the principle of thermal deoxidation, reboiling of the feedwater results in a better deoxidization effect, but it increases the likelihood of cavitation in the feedwater pump; therefore, deoxidizers operating under variable pressure must pay special attention to avoiding sudden pressure drops. 3.3 Regulation of the deaerator’s exhaust volume: The amount of exhaust from the deaerator is directly related to the efficiency of deoxygenation as well as economic considerations; if the opening degree of the oxygen discharge valve is too large, exhaust losses increase ； If it is too small, the deoxygenation capacity will be reduced, and its opening degree must be determined through adjustments during actual operation. Our plant’s deaerator removes oxygen from the feedwater only during the startup phase of the unit; at higher loads, the oxygen discharge valve is fully closed, and continuous exhaust takes place to the condenser. 4. Handling of abnormalities and accidents: The typical accidents that occur during deaerator operation include pressure and water level abnormalities, as well as deaerator vibration. 4.1 Abnormal deaerator pressure is characterized by sudden increases and decreases in pressure. The reasons for the sudden pressure increase could be a sudden drop in the water inflow to the deaerator, the unit operating under overload, high drainage volume from the superheater, or a malfunction of the pressure control valve in the deaerator. When a sudden pressure increase occurs, the cause should be investigated immediately and appropriate action taken; if necessary, the pressure in the deaerator can be adjusted manually to prevent it from operating under excessive pressure. When the pressure in the deaerator drops suddenly, it is necessary to immediately check whether the water inflow rate, pressure, and load of the deaerator are appropriate ； If the heating steam source is auxiliary steam, pay attention to monitoring whether the auxiliary steam pressure control valve is operating properly; it can be adjusted manually if necessary. 4.2 Abnormal deaerator water level: Abnormal changes in the deaerator water level are mainly caused by an imbalance between the inflowing and outflowing water, as well as sudden changes in the pressure inside the deaerator ； At this point, the main factors should be identified and addressed accordingly; adjustments should not be made blindly to prevent the deaerator from filling with water. 4.3 During normal shutdown of the deaerator, as the unit load decreases, the pressure, temperature, and water inflow rate of the deaerator gradually drop. When the load falls to 20%, the steam supply to the deaerator is switched to auxiliary steam, allowing the deaerator to operate at a constant pressure of 0.147 MPa. It also monitors the water level, pressure, and temperature of the deaerator to ensure they are appropriate for the unit’s load; as needed, it reduces the water supply to the deaerator to zero and shuts down the deaerator heating device. VI. When the deaerator is shut down for maintenance for a period of up to one week, it is possible to slightly open the backup steam supply and close all other steam and water inlet and outlet valves in order to provide thermal protection; the internal pressure can be maintained at 0.02 MPa. In the event of a prolonged shutdown (more than one week), any accumulated water inside should be drained to apply nitrogen protection, maintaining a nitrogen pressure of 0.02 MPa, or other protective measures should be taken (such as drying out the container and adding preservatives). To prevent the inner wall of the deaerator from being eroded by oxygen or other harmful gases.