Principle of deaerator

The deionized water from the pipeline system passes through a heat exchanger for heat exchange, then enters the deaerator. There, it is sprayed out through nozzles or porous tubes to form an umbrella-shaped water film, which undergoes mixed heat and mass transfer with the heating steam coming from below; as a result, the feed water quickly reaches the saturated temperature at the operating pressure. At this point, most of the dissolved oxygen and other gases in the water are essentially removed, achieving the purpose of deoxygenation. The dissolved oxygen and other gases that precipitate from the water are continuously removed from the deaerator through the steam exhaust pipe at its top, along with the remaining steam.

The deionized water is heated and flashed, and any small amount of oxygen or other gases dissolved in the deionized water are carried away by the steam； Key control points: 1. Control the high temperature so that the deionized water is close to its boiling point, in order to reduce the solubility of oxygen in water ； 2. Control the amount of gas released; there are two approaches for this: a) Control the flow rate of heating steam so that the deaerator releases only a small amount of steam, thereby reducing the oxygen partial pressure and allowing oxygen to be desorbed from the demineralized water ； b. Control the flow rate of inert gas so that the deaerator releases a small amount of inert gas, thereby reducing the partial pressure of oxygen and enabling oxygen to be desorbed from the demineralized water ； Power plants generally use the steam deoxidation method, namely option A ； Conditioned chemical plants use high-purity nitrogen to remove oxygen ；

Working Principle of Deaerator Friday, April 24, 2009, 2:54 PM The main function of a deaerator is to remove oxygen and other non-condensable gases from the boiler feedwater, in order to ensure the quality of the feedwater. If dissolved oxygen is present in water, it will cause the metals in contact with the water to corrode. Meanwhile, if gases accumulate in heat exchangers, it will increase the thermal resistance to heat transfer, thereby reducing the efficiency of heat transfer in the equipment. Therefore, the presence of any gases dissolved in water is undesirable, especially oxygen, as it poses a direct threat to the safe operation of the equipment. Thermal deaeration is employed in thermal power plants, and the deaerator itself functions as a mixed heater within the feedwater reheating system. At the same time, the drain water from high-pressure heaters, chemical make-up water, as well as high-pressure drain water and exhaust steam from various parts of the plant that meet the required water quality standards can all be directed to the deaerator for utilization, thereby reducing steam and water losses in the power plant. 1. Working principle of the headless deaerator: The main condensate water from the low-pressure heater (including make-up water), after being regulated by the inlet control valve, enters the deaerator where it mixes with other types of drain water. It is then sprayed out through nozzles or porous tubes to form an umbrella-shaped water film, which undergoes mixed heat and mass transfer with the heating steam flowing from below upward; as a result, the feed water quickly reaches the saturation temperature at the operating pressure. At this point, most of the dissolved oxygen and other gases in the water are essentially removed, achieving the purpose of deoxygenation. The dissolved oxygen and other gases that precipitate from the water are continuously removed from the deaerator through the steam exhaust pipe at its top, along with the remaining steam. Some of the water from the high-pressure heater drain that enters the deaerator will also flash vaporize to serve as a heating steam source. All of the heating steam, after releasing its heat, is condensed into condensate water, which then mixes with the deaerated water and flows downward through the outlet. To maintain the water temperature in the deaerator at the saturated temperature corresponding to the operating pressure, heating steam can be introduced into the deaerator via a reboiler tube. Deoxygenated water enters the high-pressure heater 2 via the outlet pipe after being pressurized by the feed pump. Working principle of the deaerator: (Membrane deaerator) The membrane deaerator makes use of jet and rotation technologies, as well as a packing material with a very large specific surface area – the liquid-vapor mesh box. The deaerator is designed as a two-stage deaeration structure. Level 1: The deaeration unit consists of a film-forming device and a water spray grid. The condensate water from the steam turbine, chemical make-up water, as well as various other fluids at temperatures below saturation, all flow into the water chamber of the film-forming device where they mix together. The resulting mixture then passes through the nozzles of the film-forming nozzles, which are fixed to the upper and lower tube sheets; these nozzles force the water to form a high-speed, downward-moving water film on the inner walls of the nozzles. When the downward-flowing water film comes into contact with the rising heated steam, a vigorous heat exchange process occurs. By the time the rotating water film exits the film-forming tube, the water temperature is essentially at saturation level, and 90%–95% of the dissolved oxygen in the water is removed. After flowing out of the film-forming tube, the water film forms a conical skirt, which is broken apart by gravity and the steam flow to form water droplets that fall onto the shower grates. These shower grates are composed of five layers of 30㎜×30㎜ equilateral angle steel; the deoxygenated water undergoes further heat exchange with the steam as it passes through each layer of these grates, and this process also helps to distribute the deoxygenated water evenly throughout the liquid mesh packing box. The liquid-vapor network packing box is the second-stage deaeration device in the deaerator. The liquid-vapor network packing box is designed as single-layer or double-layer depending on the actual conditions. The liquid-vapor mesh is a new type of efficient packing material; it consists of stainless steel flat wires (0.1 mm × 0.4 mm) woven into an Ω-shaped mesh. The liquid is arranged in a disc shape in its natural state, with the diameter of this disc corresponding to the inner diameter of the frame surrounding the liquid-vapor mesh. The top and bottom of the disc are fixed within the frame using flat steel bars and Φ14 rebar. As the deoxygenated water passes through this liquid-vapor mesh, it facilitates better contact between steam and water, allowing for the maximum extraction of dissolved substances from the water. This deoxygenation process ensures that the deoxygenator can operate reliably under varying conditions

This post was last edited by wavelet on 2009-10-29 at 13:04. The main function of a deaerator is to remove oxygen and other non-condensable gases from the boiler feedwater, in order to ensure the quality of the feedwater. If dissolved oxygen is present in water, it will cause the metals in contact with the water to corrode. Meanwhile, if gases accumulate in heat exchangers, it will increase the thermal resistance to heat transfer, thereby reducing the efficiency of heat transfer in the equipment. Therefore, the presence of any gases dissolved in water is undesirable, especially oxygen, as it poses a direct threat to the safe operation of the equipment. Thermal deaeration is employed in thermal power plants, and the deaerator itself functions as a mixed heater within the feedwater reheating system. At the same time, the drain water from high-pressure heaters, chemical make-up water, as well as high-pressure drain water and exhaust steam from various parts of the plant that meet the required water quality standards can all be directed to the deaerator for utilization, thereby reducing steam and water losses in the power plant. (1) Overview of the rotary film deaerator: The rotary film deaerator (also known as the membrane deaerator or water film deaerator) is a new type of thermal deaerator. It uses steam extracted from a turbine to heat the boiler feedwater to the saturation temperature corresponding to the operating pressure of the deaerator, thereby removing oxygen and other gases dissolved in the feedwater and preventing or reducing corrosion in the boiler feedwater pipes, economizers, and other associated equipment. It can operate under constant pressure or variable pressure conditions, and features stable operation, high deaeration efficiency, and good adaptability. It is suitable for deoxygenating the feedwater of various power plant boilers, industrial boilers, and thermal power plant make-up water. The improved rotary film deaerator is a newly developed deaerator with a completely different structure that has been researched and promoted in recent years. Its design involves changing the original jet-type mechanism to a swirl-membrane type; it is a high-performance new type of deaerator that combines swirl membranes with bubbling condensation. It features high deoxygenation efficiency, uniform heat exchange, low gas consumption, stable operation, good adaptability, and low requirements regarding water quality and temperature. Moreover, it can operate beyond its designed parameters. (2) Principle: The heat and mass transfer mechanism of the new type of rotating-membrane improved deaerator differs from that of existing types such as the spray tray type, water-membrane type, rotating-membrane type, and atomization type. It integrates three heat transfer mechanisms – jet flow, rotating membrane, and suspended type – into one single mechanism for heat and mass transfer, thereby achieving high efficiency. The new type of centrifugal film tube possesses high resolution capability; it causes the liquid film to rotate vigorously along the tube wall, thereby drawing in a large amount of vapor and enhancing heat exchange and mass transfer. It transforms the boiling pattern from one where bubbles form facing each other to a suspended-bubble boiling pattern, increases the vapor flow velocity in various layers, prevents splashing, and maintains the vapor channels ； The three separate heat and mass transfer devices are integrated into one, with all operations being carried out within the components of a single unit. Due to its high efficiency and certain special functional capabilities, it surpasses the technical performance of existing deaerators. Structure: The structural layout of the deaerator mainly consists of a casing, a steam-water separator, a new type of swirl film generator, a water spraying grid, a structured liquid-vapor network, and a water tank. 1. Shell: It is formed by welding a cylinder body with a stamped oval end cap. 2. Steam-water separator: This device replaces the traditional conical structure used in old deaerators, thereby eliminating the problem of water being carried away in the exhaust steam. 3. New type of swirl film former: It consists of a water chamber, a steam chamber, a film-forming tube, a condensed water connection pipe, a make-up water pipe, a drain pipe, and a primary steam inlet pipe. The rotary film tube of the new type of rotary film former is equipped with a water film guiding device, which enables strong film descent even during low-load operation, thus maintaining an optimal rotary film skirt. The condensate water and chemical make-up water are sprayed in a spiral pattern through film-forming nozzles at a certain angle, thereby creating a water film skirt. This film comes into contact with the heating steam introduced via the primary heating steam pipes, as well as the secondary heating steam that rises from the water tank through the liquid-vapor network and water grates; as a result, it is heated to a temperature close to the saturation temperature at the operating pressure of the deaerator (i.e., 2-3°C below the saturation temperature), allowing for rough deoxygenation. Generally, this membrane section can remove about 90-95% of the oxygen content in the feed water. 4. Water spraying grate: It is composed of several layers of angular steel components arranged in an interlaced pattern; the feed water, which has undergone rough deoxygenation in the deaeration section, and the steam from the high-pressure heaters are mixed here and then distributed again, falling in a uniform shower-like manner onto the liquid-vapor mesh located below it. 5. Regularized packing with liquid-vapor network: It is an SW-type corrugated packing composed of many identical open units arranged in a cylindrical shape. This regularized packing retains the advantages of wire-mesh corrugated packing and perforated-plate corrugated packing, while also featuring a larger specific surface area, lower pressure drop, greater operational flexibility, high separation efficiency, low energy consumption, and the advantage of not falling off over time. Here, the feed water comes into full contact with secondary steam, is heated to saturation temperature, and undergoes thorough deoxygenation; the deoxygenation level in low-pressure atmospheric deoxidizers is ≤10PPb, while in high-pressure deoxidizers it is ≤5PPb. 6. Water tank: The deoxygenated feed water is collected in the water supply tank located at the bottom of the deoxygenation unit. This tank is equipped with a highly efficient heat exchange and reboiling device designed using the latest scientific principles. Such a device enables effective heat exchange, rapid elevation of water temperature, more thorough deoxygenation, reduction of vibrations in the tank, and lower noise levels. These advantages extend the service life of the equipment and ensure its safe and reliable operation. (3) Working principle of the headless deaerator: The main condensate water from the low-pressure heater (including make-up water), after being regulated by the inlet control valve, enters the deaerator where it mixes with other types of drain water. It is then sprayed out through nozzles or porous tubes to form an umbrella-shaped water film, which undergoes mixed heat and mass transfer with the heating steam coming from below; as a result, the feed water quickly reaches the saturated temperature at the operating pressure. At this point, most of the dissolved oxygen and other gases in the water are essentially removed, achieving the purpose of deoxygenation. The dissolved oxygen and other gases that precipitate from the water are continuously removed from the deaerator through the steam exhaust pipe at its top, along with the remaining steam. Some of the water from the high-pressure heater drain that enters the deaerator will also flash vaporize to serve as a heating steam source. All of the heating steam, after releasing its heat, is condensed into condensate water, which then mixes with the deaerated water and flows downward through the outlet. To maintain the water temperature in the deaerator at the saturated temperature corresponding to the operating pressure, heating steam can be introduced into the deaerator via a reboiler tube. Deoxygenated water enters the high-pressure heater via the outlet pipe after being pressurized by the feed pump

Well said, learned it from *:victory:

What has been mentioned above refers only to physical deoxygenation; generally, there is also a chemical deoxygenation step, which involves adding hydrazine for a reaction with oxygen: N2H4 + O2 → H2O + N2