Deaerator

Deaerator

I. Purpose of Deaerator
The rotary film deaerator is a replacement for spray packing deaerators and represents the latest type of thermal deaerator. Its principle involves feed water being sprayed spirally at a certain angle through the film-forming tubes to exchange heat with the heating steam for deaeration. The feed water is heated to the saturation temperature corresponding to the working pressure of the deaerator, removing dissolved oxygen and other gases from the feed water to prevent and reduce corrosion in boiler feed water pipes, economizers, and other auxiliary equipment. The Ministry of Electric Power's GB1576-2001 "Safety Technical Supervision Regulations for Power Station Pressure Deaerators" sets the ministerial standard for oxygen content in deaerators: the oxygen content in feed water for low-pressure atmospheric deaerators should be less than 15 μg/L, and for high-pressure deaerators, it should be less than 7 μg/L.
II. Structure of Deaerator
The rotary film deaerator mainly consists of a shell, rotary film spray tubes, water distribution grid, packing liquid-vapor mesh, water tank, and steam-water separator:
1. Shell: Made by welding a cylinder body with stamped elliptical heads. Medium and small low-pressure deaerators are equipped with a pair of flanges connecting the upper and lower parts for assembly and maintenance, while high-pressure deaerators have manholes for maintenance.
2. Rotary Film Spray Tubes: Composed of a water chamber, steam chamber, rotary film tubes, condensate connection, makeup water connection, and primary steam inlet. The new rotary film device includes a water film guide in the film tubes, ensuring strong film formation even under low load operation, maintaining a good water film skirt. Condensate and chemical makeup water are sprayed spirally at a certain angle through the film-forming tubes, forming a water film skirt and exchanging heat with the heating steam introduced via the primary steam inlet, achieving primary deaeration. The feed water then contacts the secondary heating steam rising through the water distribution grid, heating it to near the saturation temperature under the deaerator's working pressure (2-3°C below saturation temperature) for rough deaeration. Typically, this rotary film stage removes about 90-96% of the oxygen content in the feed water.
3. Water Distribution Grid: Made of several layers of交错排列的 angular steel components, it redistributes the roughly deaerated feed water from the rotary film stage, allowing it to fall as a uniform rain-like mist onto the liquid-vapor mesh below.
4. Packing Liquid-Vapor Mesh: Composed of many identical units forming a SW-type mesh corrugated packing, creating a cylindrical body. This structured packing retains the advantages of wire mesh and sieve tray corrugated packings, offering high capacity, low pressure drop, large operational flexibility, high separation efficiency, low energy consumption, and no脱落. The thermal storage packing itself acts as a heat accumulator for secondary steam, allowing full heat exchange with the feed water for deep deaeration, achieving levels below 10 μg/L for low-pressure atmospheric deaerators and below 5 μg/L for high-pressure deaerators.
5. Water Tank: Deaerated feed water collects in the lower container of the deaerator head, i.e., the water tank. The tank is equipped with a scientifically designed strong heat exchange reboiling device, which enhances heat exchange, rapidly raises water temperature, and further deepens deaeration.
III. Working Principle of Deaerator
Condensate and makeup water first enter the water chamber of the rotary film device group in the deaerator head. Under a certain water level differential pressure, they are sprayed斜旋 into the inner holes of the film tubes, forming a jet. Since the inner holes are filled with rising heating steam, the water entrains a large amount of heating steam during jet motion (experiments prove jet motion has entrainment effects); intense mixing and heating occur over a very short distance and time, significantly raising the water temperature. The rotating water continues to spiral down along the inner wall of the film tubes, forming a rolling water film skirt (water in rotational flow has a reduced critical Reynolds number, leading to turbulent rolling). In this turbulent state, heat and mass transfer are optimal, and the water temperature reaches saturation temperature. Oxygen is separated and, unable to diffuse freely within the inner holes, is carried away by the rising steam through the exhaust pipe to the atmosphere (in old deaerators, although water was heated and oxygen separated, some oxygen, being denser than heating steam, was carried back into the water tank by descending water, contributing to poor deaeration). The roughly deaerated feed water from the film-forming stage and the drain water introduced via the drain pipe mix here for secondary distribution, falling as a uniform rain onto the liquid-vapor mesh below for deep deaeration before flowing into the water tank. The oxygen content in the tank water is 0-7 μg/L for high-pressure and less than 15 μg/L for low-pressure, meeting ministerial operating standards. Because the rotary film deaerator keeps water in a turbulent state during operation and has a sufficiently large heat transfer surface area, heat and mass transfer are efficient, with small exhaust steam volume (i.e., less steam used for heating, resulting in significant economic benefits from reduced energy loss). The excess capacity from effective deaeration allows the deaerator to operate overloaded (typically up to 50% beyond rated capacity short-term) or meet standards under full makeup water conditions with low water temperature.
IV. Installation, Operation, and Maintenance of Deaerator

1. The installation, operation, and maintenance of the deaerator, water tank, and accessories should follow the CYD(G)-type deaerator system diagram and the <>.

2. The deaerator should be placed above the feed water pump, with a height difference of not less than 6~7 meters between the lowest water level of the deaerator tank and the centerline of the feed water pump. The base plate of the tank support should have tight contact with the concrete.

3. Install temperature transmitters and flow sensors on the deaerator inlet pipe, and level transmitters on the deaerator to detect inlet water temperature, inlet water flow, and deaerator level signals. These signals are input to the computing processing module to control the hydraulic and thermal balance of deaerator water inlet and heating steam. To achieve deaeration效果, ensure deaeration temperature (104±1.5°C), adjust the electric actuator regulating valve on the steam pipeline to introduce steam for heating, automatically adjusting steam flow based on changes in deaerator water temperature. After makeup water stops, the electric actuator closes automatically.

4. A reboiling pipe is installed at the lower part of the water tank for heating and deaeration during boiler water filling and unit startup, and should be stopped after the unit is loaded. Additionally, an anti-vortex plate is installed at the water tank outlet to prevent vortex formation at low water levels,相应 increasing the effective volume of the tank. Experiments show that water vortex significantly affects pump cavitation; without an anti-vortex plate, the water tank level must be maintained at 3 times the pipe diameter height, but with it, it can be reduced to below 1.5 times.

5. After on-site welding of the deaerator and water tank, conduct a hydrostatic test. The test pressure parameters are: atmospheric deaerator 0.2 MPa, pressure deaerator 0.75 MPa.

6. Protection and Alarm for Rotary Film Deaerator

（1）Sufficient full-lift safety valves are installed on the water tank and deaerator tower, with quantity and specifications meeting design technical regulations.

（2）The rotary film deaerator should be equipped with local and remote level gauges, with high and low level alarm devices and critical high and low level action devices. Deaerator level change control: when the level drops, automatically start the soft water pump (condensate pump) to supply water to the deaerator; when the level rises, the pump automatically stops.

7. For cold start of the deaerator, preheat the shell with auxiliary steam for 15 minutes first. Under certain steam pressure, send demineralized water into the deaerator head, while regulating and increasing the steam inlet valve to heat the feed water in the film-forming stage to near the saturation temperature of the deaerator operating pressure (i.e., 102-104°C).

8. Adjust the level regulation system to maintain the water tank level within the normal level ±100 mm range. (When two deaerators need to operate in parallel, to balance pressure and level in the deaerators, steam and water balance pipes must be connectable on the oxygen water tank, ensuring尽可能一致 pressure, water temperature, and level.) When the level reaches the normal level ±200 mm, i.e., the极限 level, the high-level drain valve (electric gate valve) should open flexibly for draining and close automatically when the level drops. During operation, frequently check if the electric level regulation system operates flexibly and if the makeup water regulating valve acts flexibly.

9. Adjust the opening of the exhaust valve to achieve an exhaust steam volume of about 2-3 kg per ton of deaerated water.

10. When operating the deaerator, first open the water inlet valve, then the heating steam inlet valve; when stopping, do the opposite.

11. If exhaust steam carries water during deaerator operation, handle it by the following methods:

a. Adjust the heating steam inlet valve

b. Check the pressure adjustment device

c. Manually operate under reduced pressure

d. Gradually close the secondary heating steam stop valve.

V. General Accessories of Deaerator
· Safety Valve---Installed on the water tank, it automatically opens to relieve pressure when the internal pressure exceeds the allowed value, providing safety protection.
· Pressure Gauge---Installed on the upper part of the deaerator to monitor the internal pressure, usually of 1.5 grade type.
· Water Seal Drum---Interface installed at the high water level of the water tank; when the water level exceeds a certain limit, it automatically drains the excess part to the drain tank or ditch.
· Bimetallic Thermometer---Installed on the deaerator head and lower part of the water tank to monitor the temperature of water in the deaerator head and tank.
· Butterfly Valve---Installed on the heating steam pipeline, it regulates the heating steam flow with the help of an automatic adjuster to keep the pressure within the deaerator within the rated range.
· Stop Valve---Installed on the makeup water pipe, it regulates the makeup water flow with the help of the electric level regulation system to maintain the normal water level of the tank.
· Regulating Valve---Installed on the makeup water pipe, it regulates the makeup water flow with the help of the electric level regulation system to maintain the normal water level of the tank.
· Electrode Point Level Gauge---Installed on the water tank, it can remotely transmit signals to the control room to monitor the water level in the tank.
· Electric Gate Valve---Installed on the water tank drain pipeline, when the water level exceeds a certain limit, it automatically opens with the help of the electric level regulation system to drain the excess part to the drain tank.
· Magnetic Flip Level Indicator---Installed on the water tank, it visually shows water level changes on site and can also transmit remote signals.
· Pressure Automatic Adjuster---Automatically调节 the opening of the heating steam inlet valve, regulating steam flow and maintaining stable pressure inside the deaerator.
· Roller Device---Installed under one base of the water tank, it automatically adjusts the horizontal movement of the tank during thermal expansion and contraction.
· Electric Level Regulation System---Automatically regulates makeup water flow and controls the极限 level drain valve (electric gate valve).

VI. Data Provided for Ordering
1: Deaerator capacity (T/H) and equipped water tank effective volume (m³).

2: Deaerator working pressure and temperature.

3: For replacing only the deaerator tower, provide the installation connection diagram of the original deaerator tower.

VII. Deaerator Retrofit

Retrofit of drip tray and spray packing deaerators to film deaerators. Specifically:

1. Low retrofit cost, about 1/2 of the cost of replacing the deaerator head.

2. Fast progress, easy processing and on-site retrofit installation, i.e., using the original deaerator head's shell and head部分, removing all internal drip tray or spray packing components, retaining the lower steam inlet tray, then installing the liquid-vapor mesh and water distribution grid at a certain position above the lower steam inlet tray, and sealing and fixing with annular pressure plates to prevent water and steam short-circuiting during future operation.

3. After disconnecting the interface between the head and the cylinder, weld in the film-forming device, connect pipeline ports and other components according to the provided retrofit scheme diagram, and complete. After acceptance, put into operation.

4. During the retrofit, generally do not increase the diameter of the deaerator head; adjust its height appropriately based on specific实际情况, usually only increasing or welding according to the original height.

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