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OneSummary
Deaerators are one of the key equipment in boilers and heating systems. The severe losses caused by oxygen corrosion to boiler feed water pipes, economizers, and other auxiliary equipment annually have drawn increasing attention from the National Electricity Department. The department has issued the GB1576-2001 "Water Quality Standards for Industrial Boilers" and the "Safety Supervision Regulations for Technical Supervision of Pressure Deaerators in Power Stations," which set departmental standards for oxygen content in deaerators. Specifically, the oxygen content in the feed water of low-pressure deaerators should be less than 15 μg/L, and for high-pressure deaerators, it should be less than 7 μg/L.
The heat transfer, mass transfer methods, and deoxygenation capacity of the spiral membrane deoxygenator differ from the existing spray and spray plate deoxygenators. It is a new type of thermal deoxygenator that has won the Science and Technology Innovation Award for New Technology and New Products from the Ministry of Power.Listed as a key promotion product by the Ministry of Power.
TwoAdvantages
High deoxygenation capability, with a high qualified rate of oxygen content in the water after deoxygenation.
2: Stable operation with no vibration. Suitable for vacuum start and sliding pressure operation, reducing the need for complex manual adjustments during start-up and operation.
3: High adaptability, not strict requirements for water quality and temperature; can operate for short periods at 50% above capacity.
4: Steam volume less than 0.1% of the inlet water volume; no additional exhaust cooler required. Optimized equipment, reduced heat consumption, and consumes one-third less energy than other types of the same output deaerators.
Section 3: Structure and Principle
The structure of the rotary membrane deaerator consists of the deaerator head and the water tank. The deaerator head is composed of six main parts: the outer shell, the rotary membrane assembly, the water grating, the liquid-gas grid, the steam distribution plate, and the steam-water separator. The water tank is made up of the main body and accessories.
1. Housing: Welded from a cylinder body and a stamped elliptical end cap.
2. Membrane Assembly: Comprises of water chamber, membrane tube, condensate water inlet, and make-up water inlet. Both the membrane tube and the drain pipe are made of stainless steel, ensuring year-round operation without maintenance. It is also a major component of the rotary membrane deaerator, from which 98% of the oxygen is removed.
3. Drip Grating: The water for membrane separation deoxygenation and the condensate introduced through the drain pipes are here subjected to a secondary distribution to reduce flow, resulting in a uniform drizzle-like descent to protect the lower liquid-vapor grid. The space area of the water grate is not less than 50% of the total cross-section, made of stainless steel, and requires no maintenance throughout the year.
4. Filling Liquid-Vapor Mesh: Consists of spaced flat steel strips and a cylindrical body, internally fitted with two layers of specially designed 0.3mm O-shaped stainless steel flat wire mesh. Here, the water is in full contact with the secondary steam, heated to saturation temperature, and undergoes deep deoxygenation to ensure the oxygen content of the deoxygenated water.
5. Steam Distribution Plate: The main heating steam is introduced here, with a uniform distribution structure that ensures excellent heating quality, maintaining an even distribution of the heating steam. It rises to heat and soften water without throttling, working at saturation temperature for deoxygenation.
6. Air-Water Separator: Composed of stainless steel filling material, the inner mesh is designed with a ventilation structure, which effectively separates and returns the water carried by the steam during exhaust, making it an indispensable component for steam exhaust without water.
7. Tank: Welded from a cylindrical body and stamped elliptical end caps, internally fitted with reinforcing rings. The base is fixed to a prefabricated worktable, with one end fixed and the other for installing an expansion roller assembly. The tank is equipped with manholes for maintenance, safety valve connection ports, drain outlets, reboiling pipe openings, water seal cylinder openings, level gauge interfaces, pressure gauge openings, temperature gauge openings, and water intake ports.
The basic principle of deaerator thermal deaeration: In a container, the amount of gas dissolved in water is proportional to the partial pressure of the gas above the water surface. The main method of thermal deaeration is to use steam to heat the feed water, raising its temperature. This causes the partial pressure of steam above the water surface to gradually increase, while the partial pressure of dissolved gases decreases, causing the dissolved gases to continuously escape. When the water is heated to the boiling temperature at the corresponding pressure, the surface is entirely steam, with the partial pressure of dissolved gases at zero, and the water no longer has the ability to dissolve gases, meaning gases dissolved in the water, including oxygen, can be removed. The effectiveness of deaeration depends on whether the feed water is heated to the boiling temperature at the corresponding pressure, and also on the rate of dissolved gas removal, which is greatly related to the size of the contact surface area between water and steam.
Principle of operation of the rotary vacuum deaerator (jet, entrainment, turbulence, heat transfer, mass transfer, water film skirt, shower-like, saturated)
Condensate and make-up water first enter the internal rotating membrane assembly's water chamber of the deaerator. Under a certain differential pressure of water level, they are obliquely jetted into the inner hole from the small holes of the membrane tubes, forming a jet. Due to the inner hole being filled with rising heated steam, a large amount of heated steam is drawn into the jet during its motion (experiments have proven the jet has an entrainment effect); a violent mixing and heating action is produced in a very short travel distance, resulting in a significant increase in water temperature. As the rotating water continues to spiral down along the inner wall of the membrane tube, it forms a swirling water film skirt. (The critical Reynolds number of the water in rotational flow decreases significantly, causing turbulent rolling), at which point, the turbulent water has an ideal heat and mass transfer effect, and the water temperature reaches saturation. Oxygen is then separated out, as it cannot freely diffuse within the inner hole and must follow the rising steam out through the exhaust pipe and into the atmosphere. The water from the coarse deaeration section and the condensed water introduced from the drain pipe are mixed here for a second distribution, falling evenly like rain onto the liquid-vapor mesh below. After deep deaeration, it then flows into the water tank. The oxygen content in the water within the tank is at high pressure0-7 mg/L, pressure less than 15 mg/L meets the departmental operational standards.
Due to the vortex membrane deaerator keeping the water in a turbulent state during operation and having a sufficiently large heat exchange surface area, the better the heat and mass transfer effect, the smaller the exhaust gas volume (i.e., the less steam used for heating).Low energy loss brings considerable economic benefits; excellent deoxygenation results allow for the deoxygenator to operate at overload (usually up to 50% over its rated capacity) or to meet operating standards under low water temperature full补水.
4. Installation, Operation, and Maintenance
1. Installation, operation, and maintenance of deaerators, water tanks, and accessories should be conducted according to the CYD (G) type deaerator system diagram and the "Technical Supervision Regulations for Safety of Power Station Deaerators."
2. The deaerator should be placed above the feed pump, with the height difference between the low water level of the deaerator tank and the centerline of the feed pump not less than 6 to 7 meters. The bottom plate of the tank support should have a tight contact with the concrete.
3. Install a temperature transmitter and flow sensor on the deaerator's incoming water pipe, a water level transmitter on the deaerator, to monitor incoming water temperature, flow rate, and deaerator water level. Input these signals into the calculation and processing module to control the hydraulic and thermal conditions of the deaerator's incoming water and heating steam for optimal deaeration. Ensure the deaeration temperature is maintained at (104±1.5℃). Adjust the electric actuator on the steam pipe to regulate the valve, heating the steam, and automatically adjust the steam flow based on the temperature changes of the deaerated water. After topping up is complete, the electric actuator automatically closes.
4. The lower part of the water tank is equipped with a reboiler tube, used for heating and deoxygenating water during the boiler's filling and unit startup. When the water level in the tank exceeds half, slowly open the valve of the bottom reboiler heating tube in the tank to heat the water inside, maintaining a boiling state of the water within the tank. The reboiler should be turned off immediately after the unit starts up with load. Additionally, a prevent-rotation plate is installed at the outlet tank opening to prevent water whirl at low water levels, thereby increasing the effective volume of the tank. Tests have shown that water whirl can significantly affect pump cavitation. Without a prevent-rotation plate, the water level in the tank must be maintained at three times the pipe diameter; with a prevent-rotation plate, it can be reduced to below 1.5 times.
5. After the oxygen-removing equipment and water tank are field-welded, a hydrostatic test should be conducted. The pressure parameters for the hydrostatic test are: 0.2Mpa for atmospheric oxygen-removing equipment and 0.75Mpa for pressure oxygen-removing equipment. Steam condensate is first accumulated in an intermediate storage tank before being evenly delivered to the oxygen-removing equipment to ensure stable load operation.
6. Oxygen Scavenger with Protective and Alarm Functions
（1) Sufficient full-blow safety valves are installed on the water tank and deaerator, with the number and specifications meeting the design technical specifications.
（2) Oxygen Remover should be equipped with both local and remote water level gauges, and include high and low water level alarms, as well as high and low water level action devices. The oxygen remover's water level change control: when the water level drops, the softening pump (condensate pump) automatically starts to replenish the oxygen remover; when the water level rises, the pump automatically stops.
7. For the cold start of the deaerator, it is recommended to preheat the shell with auxiliary steam for 10-15 minutes first. Under a certain steam pressure, send the demineralized water into the deaerator head, while adjusting and increasing the steam inlet valve to heat the feed water in the film-forming section to nearly the gas saturation temperature of the deaerator operating pressure (i.e., 102-104°C).
8. Adjust the water level regulating system to maintain the water level in the water tank within ±100mm of the normal level. (When two deaerators need to operate in parallel, in order to balance the pressure and water level inside the deaerators, each deaerator tank must have a steam and water equalizing pipe that can be connected. Ensure that pressure, water temperature, and water level are as consistent as possible.) When the water level reaches ±200mm of the normal level, which is the limit level, the high water level drain valve (electric gate valve) should open freely for draining. When the water level decreases, it should automatically close. During operation, regularly check the operation of the electric water level regulating system for smoothness, as well as the operation of the make-up water regulating valve.
9. Gently open the top exhaust valve, open the valves on the steam piping, supply steam for heating, and record the steam pressure and temperature. Adjust the exhaust valve to be generally open to 2/3, so that the exhaust flow is around 2-3kg per ton of deaerated water.
10. When the deaerator is in operation, the inlet valve should be opened first, followed by the steam inlet valve for heating, and the process should be reversed when stopping.
12. During the operation of the deaerator, if water in the exhaust steam is detected, the following methods can be adopted for handling:
Adjust heating steam inlet valve
b. Inspect pressure adjustment device
c. Manual pressure reduction operation
d. Gradually close the secondary heating steam cutoff valve.
13. Test the oxygen content of the water in the sampling tank to ensure it meets the standard. If it does not, adjust the water inflow, air inflow, and exhaust gas flow to achieve compliance. Once qualified, water can be supplied to the boiler.
14. Regularly test the oxygen content of the incoming and outgoing water at specified intervals, record the readings of various monitoring instruments, to ensure the normal operation of the deoxygenator.
15. Cautionary Notes
a. When the deaerator experiences severe vibration and water ejection, water hammer has occurred; reduce the water inflow.
b. During operation, it is crucial to ensure that the pressure within the deaerator does not drop sharply, and it should not create a vacuum.
c. In case of short-term shutdown, prevent the deaerator from forming a vacuum or becoming air-filled. Gently open the bypass steam valve to introduce a small amount of steam, maintaining a heated state within the deaerator head, and expel a trace of steam from the air exhaust.
d. Regular inspections of the deaerator are required to prevent nozzle clogging, packing corrosion or compaction, and instrument failure.
e. In case the deaerator is out of service for an extended period, the water in the tank should be fully drained to prevent corrosion of the vessel.
Five, Oxygen Remover General Accessories
·Safety Valve --- Installed on the water tank, the safety valve automatically opens to relieve pressure when the internal pressure of the equipment exceeds the allowable limit, serving as a safety protection function.
·Pressure Gauge --- Installed at the top of the deaerator, monitoring the pressure inside the equipment.
Thermometer — Located below the water tank, monitoring the water temperature inside the tank.
· Butterfly valve — Installed in the heating steam pipeline, it adjusts the flow of heating steam with an automatic regulator to maintain the pressure inside the deaerator within the rated range.
· Water-seal tube --- When the liquid level rises, the pressure difference exceeds the water column pressure, causing the balance to be disrupted, and the liquid leaks out through the water seal. It also serves as a pressure relief function when the operating equipment's air pressure exceeds the safe limit.
· Stop valve --- Installed on the water replenishment pipe, it adjusts the flow of replenishing water with the help of an electric water level regulation system to maintain the normal water level of the tank.
·Adjustable Valve --- Installed on the water supply pipe, it regulates the flow of make-up water using an electric water level control system to maintain the normal water level in the tank.
·Electrical contact level monitoring---consists of a sampling tube (primary instrument) and a super-pure ceramic electrode with a display instrument (secondary instrument). Installed on a water tank, it monitors the water level inside and outputs a 4-20mA signal to the control room for adjusting the water level valve.
· Magnetic Flip Level Gauges — Installed on water tanks for on-site monitoring of the water level, and can also be connected remotely to output a 4-20 mA signal to the control room for adjusting the water level valve.
Balanced Tank — Used in conjunction with pressure/differential pressure transmitters and level gauges, it can reflect the deaerator's (weight) water level during the boiler's startup, shutdown process, and normal operation.
·Electric gate valve --- Installed on the water tank drain pipeline, when the water level in the tank exceeds a certain limit, the electric gate valve automatically opens with the help of the electric water level regulation system, discharging the excess water above the limit into the drain tank.
·Pressure Automatic Regulator---Automatically adjusts the opening of the heating steam inlet valve, regulating steam flow while maintaining stable pressure within the deaerator.
· Electric Water Level Regulation System --- Automatically adjusts the flow of supply water and controls the overflow valve at the maximum water level (electric gate valve).
Section 6: Order Provision Data
1: Oxygen scavenger output (T/H) and equipped with water tank effective volume (m³).
2: Oxygen Remover Operating Pressure, Temperature...
3: Only provide the installation connection diagram for the original deaerator tower, replacing the deaerator tower.
Section 7: Renovation
Our factory offers a complete supply of new water film deaerators while also undertaking renovations for power plants' existing spray tray and spray packing deaerators. Specifically, we focus on::
The modification costs are low, approximately half the price of replacing the deaerator head.
2. Fast progress, easy to process and on-site modification and installation. Utilize the original deaerator head shell section, remove all the spray tray or spray packing components inside the original deaerator head, retain the lower steam inlet dish, then install the liquid-gas screen and water grate at a certain position above the lower steam inlet dish. Finally, seal and secure with a circular pressure plate to prevent water-vapor short-circuiting during future operation.
3. After separating the joint between the head and the cylinder, weld and install them into the film former. Connect the other pipeline components according to the provided modification scheme, and the job is complete. Upon passing the inspection, the equipment can be put into operation.
4. During the renovation process, it is generally not advisable to increase the diameter of the deaerator head. Instead, adjust its height appropriately based on specific conditions, usually either raising or welding it to the original height.
