Heating from water to superheated steam in the boiler
Thread Content
What are the stages of heating water to superheated steam in a boiler? How does the heat absorption at each stage change with boiler parameters?
It is divided into unsaturated section, vaporization section and superheating section. Among them, the vaporization section absorbs the largest heat, and the superheating section needs to be arranged independently.
Divided into unsaturated water, saturated water, unsaturated steam, saturated steam and superheated section
The conversion process from water heating to superheated steam in the boiler goes through three stages: a. Preheating stage. The water fed into the boiler is heated to the saturation temperature under the corresponding pressure. This stage is called the preheating stage, and the heat absorbed in this stage is called preheating. This stage is completed at the bottom of the economizer, water wall and convection tube. b. Evaporation stage. The evaporation of saturated water into saturated steam is called the evaporation stage, and the heat absorbed at this time is the latent heat of vaporization. This stage is completed in the water wall and convection tube bundle. c. Overheating stage. The stage in which saturated steam continues to be heated to superheated steam is called the superheating stage, and the heat absorbed at this time is called superheated heat. This stage is completed in the superheater. The three stages of water-steam conversion are carried out continuously. The steam generated by the boiler is continuously output, and the feed water pump continuously replenishes water to the boiler to maintain the normal water level of the boiler. When the boiler is running, its pressure fluctuates with changes in external steam consumption. As steam consumption increases, boiler pressure decreases ； As the amount of steam used decreases, the pressure increases. In order to maintain pressure stability, it is necessary to adjust the boiler's combustion system in time to maintain a balance between steam production and steam consumption. It can be seen from the above that when the boiler is running, three processes are going on at the same time in the boiler, namely the combustion process of fuel, the heat transfer process of flame and flue gas to water and steam, and the heating, vaporization, separation of water and the superheating process of steam.
Among these three stages, the superheat stage is the stage that absorbs the most heat. The heat contained in the steam in this stage is also the largest, which is not proportional to the content of saturated steam.
The brother above gave a complete answer. I would like to add that the heat absorbed in the preheating stage and the gasification stage (the evaporation stage mentioned above) is basically converted into the sensible heat of the steam, while the heat absorbed in the superheating stage is converted into the latent heat of the superheated steam. This heat is much greater than the sensible heat (the sum of the heat absorbed in the preheating stage and the gasification stage). The difference between the two is an order of magnitude.
answer: The process from water heating to superheated steam can be roughly divided into three stages, namely: (1) Heating stage: Water is heated from initial temperature to boiling temperature. The liquid heat is absorbed in the economizer. (2) Vaporization stage: The conversion from saturated water (boiling water) to saturated steam and the absorption of latent heat of vaporization are carried out in a water-cooled wall or convection tube bundle. (3) Overheating stage: The saturated steam is superheated to the specified temperature. Absorption of superheated heat is carried out in a superheater or reheater. The proportion of liquid heat, latent heat of vaporization, and superheat heat absorbed from water heating to superheated steam varies with the boiler feed water temperature and steam parameters. The higher the pressure, the smaller the proportion of the latent heat of vaporization, and the greater the proportion of liquid heat and superheat heat.
It is divided into unsaturated section, vaporization section and superheating section. Among them, the vaporization section absorbs the largest heat, and the superheating section needs to be arranged independently.
1.Initial start-up: All heating surfaces are used to heat water. The mass flow rate of the pot water is equal to the mass flow rate of the feed water. 2. The working fluid temperature rises fastest at the highest heat load point of the water-cooled wall, and begins to vaporize when it reaches the saturation temperature. But the heating surface behind it is still water, and the steam will squeeze out the water behind it. The mass flow rate of the water discharged from the pot will be greater than the mass flow rate of the feed water, which is called working fluid expansion. When the pot water discharge flow returns to the same as the feed water flow, it enters the second stage. At this stage, the heating surface is divided into two sections: water heating and water vaporization. 3. In the third stage, the boiler outlet steam becomes superheated steam. At this time, the boiler heating surface is heated by water, and there are three sections: water vaporization and steam superheating.