Structural Principle
The built-in thermal deaerator uses a physical method for deoxygenation, which is carried out in two steps.
(1) Makeup water or condensate is injected into the steam space (primary deaeration).
(2) Through the steam pipe, steam passes through the water tank, carrying away the oxygen in the water to achieve deaeration (secondary deaeration).
The deaeration process of the built-in deaerator is shown in Figure 1.
1. Primary Deaeration Zone
As shown in Figure 1, makeup water or condensate is decomposed into mist-like droplets through nozzles, and the size of the droplets is adjusted according to the water flow rate to keep the droplet size constant under different flow rates. The droplets are ejected from the high-speed nozzles into the steam space in the water tank. The water is heated by contact with the steam, the water temperature rises, and the partial pressure of non-condensable gases in the water gradually decreases. The sprayed water hits the water tank baffle or water tank wall and falls, thus being collided into even smaller droplets.
The water droplets stay in the steam space for less than 1 second. In the steam space, a continuous supply of steam ensures a sufficiently high partial pressure, while the partial pressure of local non-condensable gases remains very low. When water droplets pass through the higher-temperature steam, condensation occurs on the droplet surface, raising the droplet's temperature. This heating process is completed quickly due to the large contact area of the water droplets. After the water droplets enter the steam space, the pressure of local non-condensable gases in the steam is very low compared to their concentration in the water. This lower local pressure caused by the temperature increase and the reduced solubility of non-condensable gases in water force them to separate.
2. Secondary Deoxygenation Zone
Because the water's residence time in the steam space of the spray zone is short, it may be difficult to achieve the desired deoxygenation effect. Therefore, a porous steam exhaust pipe is installed in the lower space of the deaerator water tank. Residual non-condensable gases are carried away by the steam discharged through the exhaust pipe as it passes through the water.
When steam bubbles pass through the water, according to Raoult's law, an interphase equilibrium is established between the gas within the steam bubble and its neighboring insoluble gases. Achieving this balance requires sufficient contact time. Therefore, the internal structure of the equipment is designed to generate small bubbles with a sufficiently long travel distance in the water. This is achieved by designing the size, number, and arrangement angle of the small holes in the steam pipe. The second function of the steam pipe is to enable the deaerator to start quickly, ensuring the effluent water quality reaches design requirements in the shortest possible time. Compared to any other steam heating method, the advantage of the steam pipe at the bottom of the water tank is that it ensures thorough deoxygenation of the water in the tank.
Constant-speed nozzle
Constant-speed nozzle is a crucial component of the built-in deaerator, directly impacting the quality of the deaerator's output water. The constant-speed nozzle consists of two opposing disc-shaped elastic elements clamped together. When the internal pressure of the nozzle increases, the disc-shaped elastic elements warp elastically, causing water to spray out from the gap between the clamps, forming a water film. This film is broken and agitated by the serrated structure at the nozzle's meshing point, forming small water droplets and creating a mist. The nozzle cross-section varies with the flow rate, but the flow velocity remains essentially constant within the 10%~110% range of the nozzle's rated flow rate, resulting in stable water film atomization.
