Image and Description Details Product details
I. Overview
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 each year have drawn increasing attention from the National Electricity Department. The department has issued GB1576-2001 "Water Quality Standard for Industrial Boilers" and "Technical Supervision Regulations for Safety of Pressure-Driven Deaerators in Power Stations," establishing departmental standards for oxygen content in deaerators, i.e., the oxygen content of feed water for low-pressure deaerators should be less than 15 μg/L, and for high-pressure deaerators, less than 7 μg/L.
The heat transfer, mass transfer methods, and deoxygenation capacity of the spiral membrane deoxygenator differ from those of the existing spray and spray plate deoxygenators. It is a new type of thermal deoxygenator, which has won the New Technology and New Product Innovation Award from the Ministry of Power and has been listed as a key promotion product by the Ministry.
II. Advantages
High deoxygenation capacity, 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 beyond capacity by 50% for short periods.
4: Steam exhaust volume less than 0.1% of the incoming water volume; no additional exhaust cooler required. The equipment is optimized, reducing heat consumption by 1/3 compared to other types of thermal deaerators with the same output.
Section 3: Structure and Principle
The structure of the rotary membrane oxygen remover consists of the oxygen removal head and the water tank. The oxygen removal head is composed of six main parts: the outer shell, the rotary membrane assembly, the water grate, the liquid-gas screen, 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 the cylinder body and stamped elliptical end caps.
2. Membrane Unit: Comprised of water chamber, film-forming tube, condensate water connection, and make-up water connection. Both the film-forming tube and drain pipe are made of stainless steel, ensuring year-round operation without maintenance. It is also a key component of the rotating film deaerator, from which 98% of the oxygen is removed.
3. Water Spraying Grating: The water for oxygen removal in the membrane-forming section and the condensate introduced from the drain pipes are reduced in flow and redistributed here, resulting in a uniform rainfall-like descent to protect the lower liquid-vapor grid. The grating's open area is not less than 50% of the total cross-section. Made of stainless steel, it operates year-round without the need for maintenance.
4. Filling Liquid-Gas Mesh: Composed of spaced flat steel strips and a cylindrical body, it houses two layers of specially designed 0.3mm O-type stainless steel flat wire mesh. Here, water comes into full contact with the secondary steam, heating it to saturation temperature and performing deep deoxygenation to ensure the oxygen content of the deoxygenated water.
5. Steam Distribution Plate: The main heating steam is introduced here, and the uniform distribution structure ensures excellent heating quality, making the heating steam uniformly distributed. It rises to heat softened water under non-restrictive conditions, working at saturation temperature for deaeration.
6. Air-Water Separator: Composed of stainless steel packing, the internal network is designed with a ventilation structure, which effectively separates and recirculates water from the exhaust gas, making it an indispensable component for ensuring exhaust gas is water-free.
7. Tank: Welded from a cylindrical body and a stamped elliptical head, internally equipped with reinforcing rings. The base is mounted on a prefabricated worktable, with one end fixed and the other for installing an expansion roller assembly. The tank is equipped with a manhole for maintenance, a safety valve connection, a drain outlet, a boiling tube opening, a water seal cylinder opening, a level gauge interface, a pressure gauge port, a temperature gauge port, and a water intake.
The basic principle of thermal deaeration in oxygen removers: 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 feedwater, 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 its boiling point at the corresponding pressure, the surface is entirely steam, and the partial pressure of dissolved gases is zero, meaning water no longer has the ability to dissolve gases, including oxygen. The effectiveness of deaeration depends on whether the feedwater is heated to the boiling point at the corresponding pressure and on the rate of dissolved gas removal, which is greatly related to the contact surface area between water and steam.
Principle of Operation for Spiral Membrane Oxygen Remover (jetting, entrainment, turbulence, heat transfer, mass transfer, water film skirt, showering-like, saturated)
Condensate and make-up water first enter the water chamber of the internal spiral membrane unit in the deaerator, and under a certain pressure difference, they are obliquely sprayed from the small holes of the membrane tubes towards the inner cavity, forming a jet. Due to the inner cavity being filled with rising heated steam, the water in the jet motion draws in a large amount of heated steam (experiments have proven the jet motion has an entrainment effect); a violent mixing and heating effect is produced over a very short distance, resulting in a significant increase in water temperature. The rotating water continues to spiral down along the inner wall of the membrane tube, forming a swirling water film skirt (the critical Reynolds number of the water in the rotating flow decreases significantly, causing turbulent swirling). At this point, the turbulent state of the water has an ideal heat transfer and mass transfer effect, and the water temperature reaches the saturation temperature. Oxygen is then separated out, as it cannot diffuse freely within the inner cavity and can only rise with the steam through the exhaust pipe and into the atmosphere. The feed water from the rough deaeration section and the condensate introduced through the drain pipes are mixed here for a secondary distribution, falling uniformly like rain onto the liquid-vapor net below, and then undergo deep deaeration before flowing into the water tank. The oxygen content in the water within the tank is less than 7 μg/L at high pressure and less than 15 μg/L at low pressure, meeting the departmental operational standards.
Due to the vortex membrane oxygen-removing unit keeping the water in a turbulent state during operation and having a sufficiently large heat exchange surface area, the better the heat transfer and mass transfer efficiency, the smaller the exhaust gas volume (i.e., less steam used for heating, resulting in reduced energy loss and considerable economic benefits). The excellent oxygen-removing effect allows the unit to operate beyond its rated capacity (usually up to 50% over its rated output) or achieve operating standards under full water replenishment at low water temperatures.
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 "Safety Supervision Regulations for Deaerators in Power Stations."
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 be in firm contact with the concrete.
3. Install temperature transmitters and flow sensors on the deaerator's inlet water pipe, a water level transmitter on the deaerator, to monitor signals such as inlet water temperature, flow rate, and deaerator water level. Input these signals into the calculation processing module to control the hydraulic and thermal balance of the deaerator's water inflow and heating steam. This ensures the desired deaeration effect, maintaining the deaeration temperature at (104±1.5℃). Adjust the electric actuator regulating valve installed on the steam pipeline to control the steam flow, which adjusts automatically based on the water temperature in the deaerator. Upon completion of water topping up, the electric actuator automatically shuts off.
4. The lower part of the water tank is equipped with a reboiling tube, which is used for heating and deoxygenation during the boiler's water filling and unit startup. When the water level in the tank exceeds half, slowly open the reboiling heating tube valve at the bottom of the tank to heat the water inside, maintaining a boiling state. The unit should cease using it once the startup with load is complete. Additionally, a prevent-rotation plate is installed at the outlet tank opening to prevent whirlpool formation at low water levels, thereby increasing the effective volume of the tank. Tests have shown that water whirl has a significant impact on pump cavitation. Without a prevent-rotation plate, the water level must be maintained at three times the pipe diameter; with the plate, it can be reduced to below 1.5 times.
5. After the deaerator and water tank are field-welded, a hydrostatic test should be conducted. The pressure parameters for the test are: 0.2 Mpa for atmospheric deaerators and 0.75 Mpa for pressure deaerators. The condensate steam is first accumulated in an intermediate storage tank before being evenly sent to the deaerator to ensure stable deaerator load.
6. Protection and Alarm for the Rotating Membrane Oxygen Remover
(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 Scavenger Membrane should be equipped with both local and remote water level gauges, along with high and low water level alarms and safety high and low water level actuating devices. The control of the oxygen scavenger's water level: when the water level decreases, the softening pump (condensate pump) automatically starts to replenish the oxygen scavenger; 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 feedwater in the film formation section to nearly the steam saturation temperature of the deaerator operating pressure (i.e., 102-104°C).
8. Adjust the water level regulation system to maintain the water level in the reservoir within ±100mm of the normal level. (When two deaerators need to run in parallel, to balance the pressure and water level within the deaerators, each deaerator reservoir must have a connecting pipe for steam and water to equalize. Aim to make pressure, water temperature, and water level as consistent as possible.) When the water level reaches ±200mm from the normal level, the high-level drain valve (electromagnetic gate valve) should be able to open freely for draining. It should automatically close when the water level decreases. During operation, frequently check the responsiveness of the electromagnetic water level regulation system and the flexibility of the make-up water regulating valve.
9. Slightly open the top exhaust valve, open the valves on the steam pipeline, heat with steam, 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 operating, the inlet valve should be opened first, followed by the steam inlet valve for heating. When stopping, the sequence is reversed.
12. When operating the deaerator and water in the exhaust steam is detected, the following methods can be used to address the issue:
Adjust the heating steam inlet valve
b. Inspect pressure adjustment device
c. Manual pressure reduction operation
d. Gradually close the secondary heating steam cut-off valve.
13. Test the oxygen content of the water in the sampling tank to ensure it meets the standards. If it doesn't, adjust the water, air, and exhaust flow rates to achieve compliance. Once合格, you can supply water 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 deaerator.
15. Cautionary Notes
When the deaerator experiences severe vibration and water ejection, water hammer has occurred. Reduce the water inflow.
b. During operation, attention should be paid to ensure that the pressure within the deaerator does not drop sharply, nor should a vacuum occur.
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. If the deaerator is out of service for an extended period, the water in the tank should be drained completely to prevent corrosion of the vessel.
Five, Oxygen Remover General Accessories
· Safety Valve --- Installed on the water tank, it automatically opens to relieve pressure when the internal pressure of the equipment exceeds the allowable limit, serving as a safety protection.
Pressure Gauge — Installed at the top of the deaerator, monitoring the pressure inside the equipment.
Thermometer — Located at the bottom of the water tank, monitoring the water temperature inside.
· Butterfly Valve - Installed in the heating steam pipeline, it adjusts the flow of heating steam with the help of an automatic regulator to maintain the pressure in 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 to flow 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 replenishment pipe, it adjusts the flow of supply water using the electric water level regulation system to maintain the normal water level of the water tank.
·Adjustable valve—mounted on the topping-up pipe, it regulates the flow of topping-up water using an electric water level control system to maintain the normal water level of the tank.
Electrical contact liquid level monitoring is composed 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 4-20 mA signal to the control room to regulate the water level valve.
· Magnetic Flip Level Gauge --- Installed on the water tank for on-site monitoring of the water level inside, also capable of connecting remotely and outputting 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 outlet pipeline of the water tank, when the water level in the tank exceeds a certain limit, the electric gate valve automatically opens with the aid of an electric water level regulation system, and the excess water above the limit level is drained into the overflow tank.
· Pressure Automatic Regulator --- Automatically adjusts the opening of the steam inlet valve, regulating steam flow while maintaining stable pressure inside the deaerator.
· Electric Water Level Regulation System — Automatically adjusts water supply flow and controls the discharge valve (electric gate valve) for maximum water level.
Section 6: Order Provision Data
1: Oxygen removal capacity (T/H) and the effective volume of the water tank (m³).
2: Oxygen separator working pressure, temperature...
3: Only replace the oxygen-depletion tower and provide the installation connection diagram for the original oxygen-depletion tower.
Seven, Renovation
Our factory not only supplies complete sets of new-type water film deaerators but also undertakes renovations for power plants' spray plate and spray packing deaerators. Specifically, this includes:
Low modification costs, approximately half the price of replacing the deaerator head.
2. Fast progress, easy to process and on-site modification installation. Utilize the original deaerator head's shell section, remove all the spray disk or spray packing components inside the original deaerator head, retain the lower steam inlet disk, then install a liquid-gas mesh and a water grate at a certain position above the lower steam inlet disk. Finally, seal and secure it with a circular pressure plate to prevent water-vapor short-circuiting during future operation.
3. After separating and welding the flange from the cylinder, install it into the film former. Connect the other components at the pipe opening according to the provided modification plan, and the job is complete. Upon passing the inspection, the equipment can be put into operation.
4. During the改造 process, the diameter of the deaerator head is generally not increased; instead, its height is appropriately adjusted based on the specific circumstances, usually either raised or installed and welded at the original height.
